This to a newcomer seems like a good idea, applying some extra protection equipment to the display aquarium and avoiding the need for a separate tank with the consequent need for extra heating, power heads and the like. Closer examination seems to be in order.

What is a quarantine tank? This is a smaller aquarium that is kept in addition to the display aquarium. Its purpose is to welcome new fish additions (and corals etc  in many cases). The new arrivals are kept in quarantine for a minimum of two weeks, better four, so that any problems caused by the stress of transportation etc come to the surface and can be treated in isolation. If certain diseases raise their unwanted heads, then copper for example can be used, whereas in a reef aquarium it cannot as it is deadly to corals. In other words, newcomers are kept in isolation so that existing inhabitants of the display aquarium are not exposed to problems that could exist. Once the quarantine period is over and the aquarist is satisfied that all is well, the newcomers can be transferred to the display aquarium and the danger of problems is minimized.

The UV (ultraviolet) sterilizer is a piece of equipment that, as the name implies, helps to eradicate undesirable live content in the water – let’s just call the undesirables ‘nasties’. These could be bacteria or the spores of disease, mainly of the commonly called ‘white spot’ and ‘velvet’. What happens is that the water is pumped through the sterilizer, which is usually cylindrical. There is an outer wall and an inner one which contains the light, between is a thin gap. As the water moves through this gap life is exposed to the radiation and killed, or damaged to an extent that the ability to reproduce is severely impaired. It is very important that the water is pumped at the correct speed through the sterilizer so that there is sufficient exposure to the radiation, so the manufacturer’s recommendations need to be followed. It is also important that the given life of the UV bulb is not exceeded or the effectiveness of the unit will be reduced. Finally, the sterilizer should be sized to the gallonage it has to deal with.

So on the face of it the sterilizer could replace the quarantine tank (QT). It does exactly what is required, that is it destroys or damages unwanted nasties in the water. So there isn’t a need to keep fish in a QT as any nasties will be destroyed anyway. If only it was as simple as that, but it isn’t.

For the water to be pumped through the sterilizer there obviously has to be an intake. Logically the intake needs to be in an area where most water is likely to pass, so it needs to be where there is considerable circulation. So far, so good. Does this actually mean all nasties in the water will be sucked in and destroyed? Unfortunately it doesn’t.

In most modern aquaria, particularly reefs but also fish only, there is considerable decoration such as rocks or their substitues. This means that water will have quiet spots behind and under rocks or even just close to rocks. The method of reproduction of certain nasties is quite sneaky. They attach to fish where an aquarist can hopefully see them, then they drop off and go down into rocks etc. They then reproduce by division and where there were only a few there are soon many more. In the confines of an aquarium there can soon be high and increasing numbers. The point is that it is very likely that quite a lot of these nasties are going to be drawn into the steralizer, but not all. The ones left will reproduce and the problem can increase despite the presence of the sterilizer.

There has to be a QT then? The answer is yes, but there are considerable numbers of aquarists who seem to rely on luck and perhaps good judgement. The good judgement is choosing the source of their livestock and noting the condition of it, and the luck is that they were, well, lucky. By placing new fish straight into a display aquarium they are putting at risk the health of the livestock already there. Nowadays with better transport facilities and more knowledgeable dealers livestock should be in better condition, but there isn’t any guarantee of this, the danger of problems is ever present. There should be a period when a QT is put to use.

So the UV sterilizer is a waste of money then? No it isn’t, but it isn’t an essential either. The protein skimmer is viewed as an important assistant to the maintenance of high quality water. The sterilizer should be viewed in a similar way but with regard to health. The sterilizer is lower down the list of importance than a protein skimmer.

There isn’t any reason why a sterilizer shouldn’t be used if desired. It will help to destroy unwanted nasties and maintain health, or assist in the battle against existing disease. However, it is an aid to a healthy aquarium environment, not a guarantee of it.

If the aquarist maintains high quality water, provides a good diet and doesn’t overstock then there is a good chance of continuing good health. A UV sterilizer could be an aid but is not an essential as is for example a protein skimmer. If a QT is also used the potential for ongoing health is greatly enhanced.

All marine aquarists are aware of live rock. It’s the stuff that perhaps the majority use for bio- filtration and it’s also excellent as décor, be it a reef or a fish only system.

Good mature live rock has the usual bacteria present, those that convert the toxins ammonia and nitrite to the much safer nitrate. Unlike a canister filter where the nitrogen cycle stops after the production of nitrate, live rock within reason will deal with nitrate. This is because the bacteria that dwell deep inside the rock would also prefer to use oxygen directly, but because it is in very short supply they remove oxygen from nitrate which breaks it down.

When I set up my current soft coral reef system I used two canister filters for the bio-filtration. (The photo shows the reef in part. You can tell I took the photo!) The bio- media was Eheim sintered glass. It worked very well. Being aware that nitrate could become excessive I built a denitrator based on suphur and this ran from when nitrate was noted as being present even though the reading was very low. Better to defeat a potential problem than wait to tackle a real one. Once the denitrator was matured the nitrate disappeared and I never had any readings at all. This was over the first 5½ years of the aquarium’s life. It has to be said that the fish load is very low; there are two small fish (a blue damsel and a flame angel) in 43 gallons net of seawater.

The reef is built of what is named ‘grotto rock’. This doesn’t come from any grotto so why the name I don’t know, however it’s ideal for marine use as it is totally inert and full of crevices and holes. Just as important, it’s very porous. The rock comes in all sorts of shapes and sizes and it was great fun creating the reef.

The reef developed over the years and I noted the lack of nitrates. I thought I’d do a little experiment at one point to prove the effectiveness of the denitrator; this experiment consisted of turning if off. Difficult!

I monitored the nitrate level and found that all readings were zero (I suppose I ought to state that nitrate was undetectable with the test kit). I left the denitrator off for a week, two weeks, which turned into months. Still nitrate didn’t appear. The canister filters continued to run so nitrate would be produced.

I like looking at the reef from various points in addition to the front and sides. This often involves lying on the floor and peering into the aquarium. This sometimes occurs at night when most of the little beasties are about. The rocks I thought looked more like live rock than the real stuff, with all the worm growths, algae etc. I then wondered if it was in fact live. This thought was supported by the lack of nitrate, the canisters were producing it and perhaps bacteria were removing it? I realized that I did routine seawater changes and this would tend to reduce nitrate levels as well.

The rocks were now live, why not? It was an excellent home for bacteria after all. However, at the end of the day a rock looks like a rock, there’s no way a bacteria presence can be checked. It is a known fact that bacteria exist on surfaces within the aquarium in addition to any intended bio-filtration area, but would there be sufficient to support the aquarium completely? Surely the canister filters would be taking the majority of the bio-load?

I have two canister filters running as said, so it was easy to check. At the next scheduled clean of one of the canisters I removed the bio-media and ran the canister empty (seawater is returned to the surface for oxygenation and to agitate the surface). A careful watch was kept and there weren’t any unwanted effects.

So far so good, but the next stage was a little more cautious. Even though the bio-media from the first canister had gone, maybe the second canister was handling everything, so with the second canister, when the time was chosen to remove some bio-filtration media I only removed half of that present. Hopefully that left would prevent any major disaster from occurring. The amount left was one quarter of the total original amount. This was left for a month with everything being carefully watched. No problems.

Now came the crunch – remove the final bio-media. This was done and both canisters now ran empty. Feeding and maintenance continued as though nothing had changed. Nothing untoward happened.

The system continues to run normally and it is now approaching its 7th year. The inert rock is now live.

To be honest I wasn’t really surprised, though it was very sound to use caution. One way of producing live rock is to mix inert rock in with live; the higher the live proportion the quicker the inert variety converts (it still takes quite some time). There wasn’t any live rock in the system at all at the start; it was all inert, so how did it convert?

The first possibility is that ‘overspill’ from the canisters occurred though perhaps this is unlikely, I don’t know. The second is that bacteria developed on and in the rocks naturally and these expanded in number.

To my mind the most likely explanation is that the bacteria were introduced, though some could have appeared naturally as suggested above. Most of the corals that were introduced are attached to rocks and of course they were attached to these when collected – these rocks are live. So the inert rocks were colonized by the bacteria from the live coral rocks.

When the bio-media was slowly removed from the canisters the bacteria on and in the rocks would have expanded to deal with the increased load and, hey presto, the system is now based on live rock.

The denitrator sulphur media has been cleaned and is not in use. I haven’t actually removed the unit as it isn’t in the way. The good thing is there isn’t any more need for it to be maintained though the maintenance wasn’t a problem. The worst part was the flow, denitrators have a very slow flow and this was occasionally problematical and a bit of a headache. No more of that though.

Many modern marine aquariums use ‘natural’ methods as much as possible. This has been achieved by the advances in knowledge that have been made over the last few years.

Some aquarists argue that it is impossible to keep an aquarium without using natural methods and I can see where they are coming from. The point they have in mind is bio-filtration, all those hard working bacteria getting rid of the toxins in the seawater. Without them we’d be in a sorry state. It’s true as well that this filtration is natural. However, if the bacteria colonies are housed in a canister filter then it isn’t completely natural, the home for the bacteria is being provided by our technology. Nothing wrong with that as it stands.

A fully natural method for bio-filtration, staying with the example, is live rock. This rock mainly comes from the wild and has bacteria present. It is a really good filtration media and, unlike the canister filter, within reason the bacteria can deal with nitrate as well. Can’t be bad!

There are new commodities on the market that are designed to replace live rock. This is a rock that appears very similar to the fully natural variety but needs the bacteria colonies kick starting in the same way a canister filter does. One running the new rocks are suitable homes for all bacteria including those that deal with nitrate. This isn’t removing ‘natural’ filtration; the difference is purely the type of rock. There isn’t any electric motor required. It also reduces the demand from the wild, unless the live rock is aquacultured in the wild.

Anyway, getting back on track, there are a few ways that an aquarist could use natural methods. Think of filtration by algae, deep sand beds, plenums, mangroves etc.

The link below is to a website article where natural methods are definitely in mind.

http://www.practicalfishkeeping.co.uk/pfk/pages/show_article.php?article_id=551

There are two Eheim Ecco canister filters installed and I have to say that they are good, well constructed and to date absolutely reliable. Anyway that’s not what I’m on about here.

Over the six years many corals on rocks have been introduced and the rock that was inert and dead is now live. It hasn’t the potential diversity of life that natural live rock has, but it has a lot of organisms on it and probably in it – there are tiny tube worms by the hundred and a high population of tiny creatures that appear mostly at night. It is also typical live rock in appearance as far as encrusting algae and the like are concerned. I have to say I can’t see that much rock anyway as most is covered up by some organism or another.

I suspected that the rock was live because of nitrate. As I had elected to use canister filters a home made denitrator had been fitted as well. There has only ever been the tiniest presence of nitrate according to the tests and it was so faint my wife and I were unsure about that. Eventually this trace disappeared as well and never re-appeared. So about two years after the trace, if there was one, had disappeared I turned the denitrator off. There continued to be no trace whatsoever of nitrate and the denitrator has remained off.

If there was nitrate present and it had disappeared then routine seawater changes wouldn’t have been the cause as these have been done bi-weekly ever since the aquarium started (though at first they were weekly). It wasn’t the denitrator as this was turned off and nothing re-appeared. I assumed that bacteria had colonized the very porous reef rocks and these were dealing with any nitrate, as well as ammonia and nitrite. I decided to remove the bio media from one of the canisters. It didn’t happen.

The canisters, both of them, were left running in full bio-mode as I didn’t do anything because of the reef, it was so successful and natural looking that I was afraid that if I made a mistake the livestock would suffer and I wouldn’t have time to generate a new bacteria population. After a while, I thought that this was ridiculous – and it was as there are two canisters and they both have the capacity to bio-filter the aquarium. So I removed the media from one, then started it up again empty as it is used for surface agitation.

To date, six months down the line, there hasn’t been a problem. So now I’m thinking I’ll remove the bio-media from the other canister. Going on previous performance it’ll be a while before anything is done! I feel certain that there isn’t a need for bio-filtration with the canisters any more.

When I removed the bio-media I expected that there would be visible life within it (Eheim sintered glass). There wasn’t, none at all, at least any I noticed. The aquarium is full of life, mobile and otherwise, so this was a surprise. On cleaning mechanical media I am always rescuing tiny shrimps.

I was really pleased with the state of the bio-media. When washed only a very small dusting of dirt appeared, one rinse and it was gone. This was down to the four weekly mechanical media cleaning, also the mechanical media set-up. The entire mechanical media was before the bio-media, taking the form of a coarse sponge, a very fine filter ‘cloth’ one half inch thick and another fine sponge, so the filter ‘cloth’ was sandwiched tightly between the sponges. It clearly worked.

During the operation on the canister I noticed a fair growth of some toadstools in one area on the reef. All the corals grow at a quite fast rate and the toadstools are the fastest. So out came the sharp scissors and off came their heads. Very drastic sounding but it has been done several times before without mishap. They grow back rapidly.

I also noticed more new corals growing beneath, toadstools again, six in all. Four were removed entirely and two left. The photo (sorry, it isn’t particularly good) shows the cut ‘stalks’ and also the two small new ones that were left.

The cut corals look awful at first but they don’t stay that way for long. First polyps re-grow, then the heads start to increase horizontally and the stalks lengthen.

It’s all quite miraculous really.

The first negative is that it is expensive and it’s bound to be with the cost of air freight never mind transport to the final destination in the US or Europe. This cost is generated by both weight and bulk.  Nevertheless, aquarists buy it and can reduce their costs by using base rock underneath the reef which is less expensive. Another way is to reduce the amount required by putting face rock on a framework of plastic supports which means less is required, though care has to be taken that there is still an adequate amount for effective bio-filtration.

Some enterprising aquarists manufacture their own live rock though the numbers who do this are low and the result is not usually as good looking as the real stuff (in my opinion).

Other aquarists use dead inert rock as a reef and employ canister filters for the bio-filtration. This is what I did with my current reef. The bio-media is being removed from the canisters as the rocks are now live.

The last paragraph leads me into the reason for this text. My aquarium (over six years old) is now using rocks as its main bio-filtration, as said the rocks were previously ‘dead’. After setting up the aquarium, before the canisters could be used they had to be ‘matured’, that is a bacterial culture had to be started within them. It could have been done another way – I could probably have used maturation fluid to establish a bacteria colony on the rocks in the first place, they are very porous. The rocks when used initially were not very ‘reefy’ looking though they are now.

If only there were rocks that were both porous and ‘reefy’ in appearance many aquarists would be pleased. Well, it seems there are now.

Artificial ceramic reef ‘rocks’ were brought to my attention by a comment on the forum, they are named Vida Rocks. So of course, never having heard of them, I went onto the internet and had a look. I have to say that the appearance of the rocks seems good, they are natural looking taking the shape of ordinary rocks, arches etc. An aquarist would be able to create a good looking aquascape with them.

The rocks are stated to be highly porous. This means that they should present a suitable habitat for those bacteria that protect our livestock. The bacteria culture would have to be kick started in the same way that a canister filter is by the use of maturation fluid, but this is not a problem. With this method nitrate will probably appear in the aquarium but this is easily reduced by a seawater change. As the ceramic article is porous the possibility, or maybe probability, arises that nitrate could be dealt with as with natural live rock. Bacteria could establish inside the rock in low oxygen areas. It would be great if this occurred.

So we have a system that will present an ‘authentic’ reef appearance and provide adequate bio-filtration. Over time the rocks will become more natural looking as organisms take over the surface areas. These organisms could be introduced on rocks with corals attached.

There must be disadvantages though, and there are. The ceramic rock is not loaded with bacteria by Mother Nature as the natural stuff is. Also, the life forms that could appear in the aquarium when using natural live rocks are not there. The life that could appear with natural rocks is a gift, and there is often quite a lot of it even after the transport time and ‘curing’ process. However, natural live rock could also bring undesirables such as aiptasia (glass anemones) etc which will obviously not occur with the ceramic type. Undesirables could appear in the course of time anyway as coral rocks will be introduced to a reef system and so the threat remains.

I am all for the move to ‘natural’ based aquarium husbandry as are most aquarists and this hasn’t changed. Live rock and deep sand beds (DSB’s) are a good example. This ceramic rock has aroused my interest. If the ceramic rock has been ‘matured’ with bacteria and is combined with a DSB it would amount to very nearly the same thing, with a difference.

The difference is that live rock for the most part is taken from the wild reef areas. By using the manufactured rock the demand on the wild resources would be reduced which generally would be good. Local fish shops (LFS’s) would probably state that it would affect their trade, so they could sell the ceramic variety. They could even sell more of it as it would no doubt be cheaper particularly as it does not have to be air freighted, at least in the US where it is manufactured (I do not know the price).

For an aquarist who is considering extending their reef (or fish only aquascape) this ceramic rock could be considered. It will need a little time to mature (bacteria) so if increased stocking is envisaged care would be needed.

For an aquarist who is just setting up a marine system it is a consideration as a particular aquascape design can more or less be achieved. The normal constraints on stocking after maturation would apply, as with a canister filter. Unlike a canister filter, hopefully the industrious bacteria within the ceramic rock would within reason have an effect on nitrate levels.

Have a look and see what you think:

http://www.cerameco.com

I look forward to comments by aquarists who use it.

(Aquaristsonline.com does not have any links, personal or commercial, with the above internet site)

In the refugium filtration method various types of macro algae are grown in the fine sand. The mud bed filtration system is effectively the same, however instead of sand mud is used instead. It is not just normal mud though, it is a mud which is full of various elements and minerals. These elements and minerals are slowly released from the mud into the water column.

A mud bed system is normally run in an aquarium or some other container located under the main display aquarium. Some aspect of mechanical filtration is required to remove any large particles from entering into the mud filtration area. This can be performed at the end of the overflow(s) by passing the water through very small chunks of live rock etc. After the water has been through the mechanical filtration it enters the mud filtration aquarium. The macro algae consume nutrients from the water and various elements are slowly released into the water from the mud bed. The water then normally passes through some type of grid or through another chamber full of small pieces of live rock the purpose of which is to prevent any of the macro algae from leaving the mud area and blocking the return pump. Once the water has passed into the pump area it is returned to the display aquarium.

In a mud based system the lights are normally left on for 24 hours a day. This allows the macro algae to photosynthesise and grow. It is only when macro algae grow that they consume nutrients from the water. It is best to use lighting which is designed for the growth of plant life. A couple of fluorescent tubes will suffice, ensure as said that they are for plant life and have a Kelvin rating of around 6000. Lights with this Kelvin rating have more colour in the yellow/red area which benefits the plants.

A normal rule of thumb for a mud based filtration system is to pass in the region of 10 times the total water volume per hour. This needs to be considered when designing the aquarium system as the total amount of water in the system will determine both the overflow size and the size of return pump required.

As with a refugium there may be a requirement to harvest the macro algae if it becomes too dense. Never pull the algae out by the roots – instead cut the plants back with an old pair of scissors or similar. Harvesting the algae will allow more light to penetrate into the areas where the algae grows. One point to remember is that you should not add this macro algae back into the aquarium as you may reintroduce the nutrients back into the water.

A mud based system combined with macro algae removes a lot of the nutrients (nitrate, phosphate etc) and dissolved organic compounds as well as replenishing trace elements.

A lot of aquarists who utilise a mud based system for filtration do not run a protein skimmer. It is not recommended to do so by these aquarists because of the amount of particulate matter which is extracted from the water by protein skimmers. When viewing a mud based system you can actually see the fine particulate matter in the water. The water is still clear, however it is full of fine matter which some life in the aquarium can use for energy.

Of course there are also aquarists who do choose to run a skimmer, however the majority of these run the skimmer part-time (i.e. throughout the night, turned on/off via the use of a timer). The majority of these aquarists decide to run a skimmer as they are very wary of turning it off. I have run a system using a mud based method combined with live rock for many years without problems. The only thing you need to ensure when you run a system like this is that detritus is removed from the main display aquarium regularly and that weekly water changes are performed. A lot of aquarists who do not run a skimmer on their mud based systems do not have a sand bed in the display aquarium due to the build up of detritus which can occur. Instead they go ‘bare bottom’ in the aquarium. The glass which is visible at the bottom of the aquarium quickly becomes covered in coralline algae as well as other types of life so looks more natural as time passes.

The aquarists who decide not to run a skimmer have reported a higher level of particulate matter visible in the aquarium water which the corals, and other filter feeders consume. Because of the amount of particulate matter in the water column you should see good polyp extension from your corals as well as hopefully having success in keeping some of the harder to keep corals. Obviously you cannot just expect to be able to keep these more difficult corals just because you are running a mud based system – you must still ensure that you have optimal water parameters and that the requirements for the livestock in question are met.

Implementing a mud based filtration system is fairly straightforward. It is best to have an aquarium which is split into three or four sections. This can be accomplished yourself using glass and baffles or you can have one made for you at your local fish shop.

The first area is where the live rock is placed and is where the water from the display aquarium, via the overflow(s), enters the filtration aquarium. The purpose of this section is to remove any large detritus from the water as well as break up any air bubbles. Using live rock in this area is a good idea rather than another type of media as it is a natural filtration medium and will actively help in filtering the water rather than hindering it as other types of media could do.

The second section is where the mud is placed as well as the macro algae (caulerpa etc). The mud is poured into this section and the macro algae planted within it. To give the macro algae a chance to put its roots down trap it gently under a piece of live rock. Once the macro algae takes hold the piece of live rock can be removed. It is advisable to add a few varieties of macro algae as some may not take root. Caulerpa is one species which does tend to do well and there are numerous varieties available. Because of the amount of water flow which can be created in the central chamber some people choose to create small containers 1 inch or so high and 1-2 inches apart in the bottom of the chamber. This prevents the mud from moving around and building up in a pile at one end of the chamber.

The third or fourth section is where the return pump is located and is protected from the second central section via a baffle of some type or even more chunks of live rock contained in a chamber. If you are running this mud aquarium as your sump then your heaters for example can also go in this area.

A couple of fluorescent tubes will suffice for the lighting above the mud section and should remain on for 24 hours per day. As said attempt to use tubes which are designed for plant life as this will help the macro algae grow.

Because of the mud releasing essential elements into the water the mud bed will eventually expire, therefore it is recommended that half of the mud bed is replaced about every two years however I would recommend that you rely upon the manufacturers recommendations in this area.

So what actually is a plenum?

A plenum is not a filtration unit but is actually a space which is located under the substrate and separates the substrate from the bottom of the aquarium.

This space (the plenum) is full of both the water and any organic waste as the water is diffused into it. A plenum is also sometimes referred to as a Jaubert system as Dr Jean Jaubert was the individual who discovered it.

The structure of a plenum is actually very very simple. It is basically a deep layer of substrate which is suspended above the bottom of the aquarium to create a space or a void if you will.

How it works is, although slightly scientific, also relatively simple.

As the water moves slowly through the substrate the nitrifying bacteria in the upper level use up all of the oxygen in the water and convert the ammonia to nitrite and then the nitrite to nitrate. The nitrate which remains is the transported with the water down towards the plenum. As the water reaches the lower levels of the substrate the nitrate is then slowly broken down into nitrogen gas by the denitrifying bacteria which live in the very low oxygen levels of the substrate.

The reason the water moves slowly through the sand is due to the anaerobic action being performed in the lower levels. The anaerobic actions produces heat which heats up the water in the plenum area. This heated water moves up through the substrate which therefore displaces the cooler water above it causing the water to move through the substrate at a very slow rate.

A slow rate of water movement is important in a plenum as it assists in the prevention of a dangerous build up of hydrogen sulphide.

The upper levels in the substrate will become home to various organisms which can either be introduced via the aquarist or are organisms which have relocated from their home in the live rock. These are very important, the same as they are in a deep sand bed. Their job is to keep the upper levels of substrate ‘turned over’ and clean from both detritus and waste.

The above is how a plenum operates but how do you actually make one.

Again this is relatively simple. Not as simple as a deep sand bed as it does require a bit of DIY but simple all the same.

The items listed below are required to make the plenum. This list is not set in stone and can be modified to suit your/the aquariums needs.

Marine safe PVC piping.
Egg crate to make the grid from.
Screening.
Aragonite based sand with a granular size between 1 and 2 mm.
Live Sand.
Silicone.
Tie Wraps.

The recommended minimum required depth of substrate in a plenum is 2 ½ inches when placed on top of the plenum grid therefore you need to ensure that you obtain enough aragonite/live sand to accomplish this.

The first thing you will need to do is actually create the support which the substrate which sit on top of and create the plenum. Personally I find that marine safe PVC pipe is the best for this. These, when laid on their side provide a lot of strength for the substrate held above it.

I would recommend that you cut this piping in lengths of two inches or so and ensure that you have enough of them to support the weight of the substrate above it. Remember that you may also be placing rock on top of the substrate in the aquarium so make enough of them to support this as well. If you are unsure make more than you think you will need.

Once all the support have been kit you will now need to make the grid. The grid is basically there to hold the substrate up and also to prevent any of the substrate from falling down into the plenum area and effectively making it useless.

The easiest way I have found to do this is use eggcrate and cut this to the same dimensions as the inner dimensions of your aquarium. It does need to be noted that the grid needs to be a very tight fit so take your time cutting it. Once cut it can then be attached to the supports. I have found that tie wraps are excellent for this.

The basic structure of the plenum is not in place, however if the substrate was to be placed into the aquarium at this point it would simply fall through the eggcrate into the void. This is where the screen is used.

Cut the screen so that it is slightly larger than the inner dimensions of your aquarium. Once cut carefully place it into the aquarium, fold up the edges and carefully silicone it to the side of the aquarium. You will need to allow the silicone to cure which normally takes about 24 hours but once cured you should have a screen which no substrate will fall through.

Once cured you will be in a position to add the lower level of substrate. Add 1 ½ inches or so of aragonite and give it a really good stir using your finger to remove as many pockets of air as possible. Also be exceptionally careful not to tear the screen otherwise all your hard work will go to waste.

Now that the first layer is in place you will need to cut a second screen to slightly larger than the inner dimension of the tank, and silicone it in place as you did the first screen.

Once the curing process is complete put another 1 ½ inches of the aragonite sand into the aquarium. As with the first layer give it a really good stir with your fingers to remove as many air pockets as possible again being careful not to damage the screen.

Now we are ready for the live sand. Add about 1 inch or so of live sand to the top of the final layer – a screen is not required this time as it does not matter if the live sand mixes with the top layer.

The plenum is now complete and ready for water. When filling with water fill it slowly to avoid creating any air bubbles and mixing all the sand up.

So now we should have a plenum area at the bottom topped with a screen, on top of this screen is some aragonite sand followed by another screen. On top of this screen is some more aragonite sand and then the live sand. All of this is supported via some pvc piping to take the weight and create the plenum space.

In a plenum system it is recommended that little or no water flow be directed across the surface of the substrate. It is also recommended that a protein skimmer be utilised with a plenum as this will assist in the removal of any dissolved organic compounds which are not removed by the plenum.

It is easier to introduce a plenum to a new aquarium rather than the modification of an existing one. If you are interested in introducing a plenum to an existing system you will either have to remove everything from the display aquarium to introduce it or build a plenum in a separate aquarium and attach it to the system using overflows and pumps.

As with the introduction of any filtration device you will need to monitor the water parameters carefully so that you know that the nitrogen cycle is functioning properly.

It still amazes me today how powerful natural aquarium filtration actually is and how many ways there are to actually filter an aquarium or provide additional nutrient export by using the power of mother nature.

Nowadays whenever I am asked for my recommendation as to the best way to filter a marine aquarium I always mention natural filtration. In my opinion and this is purely my opinion live rock mixed with a remote deep sand bed has to be the ultimate natural based filtration available at this moment in time.

The prime advantage of using natural based filtration methods is its efficiency and the advantages that it gives to the aquarist.

A lot of people however have never heard of natural filtration never mind actually understand what it is.

So what is natural filtration?

Any filtration technique applied to an aquarium actually does have an element of nature in it – the bacteria however in a lot of occasions the container upon/in which the bacteria lives is not natural – it is manmade.

A good example of the above would be a canister filter. The bacteria is natural, however the holding device if you will has been manufactured.

Therefore a good way to explain natural filtration is that it is where the bacteria live in any area which has not been manufactured by man.

This is not a set rule however as there are exceptions to natural filtration. One of which would be using macro algae as a nutrient export tool.

Numerous natural filtration methods can be employed in the home aquarium. Some can be implemented for use as a primary filtration method whilst others can be utilised as an additional nutrient export tool.

As already stated natural filtration can be and is an exceptionally powerful tool. Think about the ocean – it is huge, however the natural filtration devices which are in use in the ocean are very similar to what we can use.

The rock structures on the coral reefs are similar to live rock filtration, grass beds are similar to a refugium/macro algae, mangrove swamps are a much larger scale of mangrove usage in the aquarium etc.

Can you see how powerful this type of filtration can be. The ocean has been filtered this way for millions of years and it can and does work in the aquarium.
Although our aquarium are minute compared to the size of the worlds oceans the end result is the same – excellent water parameters.

There is a point which needs to be made however, the filtration has been termed as natural filtration simply because it is similar to what is used in nature or is the same as is used in nature but on a much smaller scale but there will always be an element of human involvement.

That’s right – the care and maintenance. As with all things in this hobby the correct care and maintenance techniques need to be applied and this is no different with natural aquarium filtration. Nature can again be involved in this area for example using hermit crabs, snails etc to keep the rocks/sand clean however there will always be a time where we need to get involved to keep it just right and running at optimum efficiency.

If you are just starting out in this hobby or already have an aquarium and are using man-made filtration then I really recommend that you at least consider natural based aquarium filtration. It is absolutely amazing how powerful it actually is.

There are two zonal categories which are most commonly used, these are the exposed and the semi exposed zones.

The exposed zone is an environment which is in shallow water and receives a lot of strong sunlight. This is the zone which is typical of the upper reef, otherwise known as a shallow reef. The water currents in this zone are normally quite fast and chaotic, therefore any organisms which live in this area have to be able to withstand such high currents. Due to the high currents there is normally a lot of suspended matter moving around in the water; however with the strong water current a lot of the filter feeding organisms struggle to extract these from the water. This zone is where the majority of the light loving high current SPS corals live and is effectively the environment which we attempt to replicate in the majority of our reef aquariums.

The semi exposed zone is similar to the exposed zone but both the light and water currents are considerably less. Because of the lower water currents filter feeding organisms are able to extract the particulate matter from the water more easily. This zone is similar to that of deeper reef conditions, and is otherwise known as the back reef. In this zone there are still a huge range of photosynthetic organisms which can survive but this zone, because of the lower light conditions, also provides the non photosynthetic organisms with a place to thrive. Again this environment can easily be replicated in our reef aquariums.

In the marine aquatic world there are effectively three more zones which are:

1. Semi Cryptic
2. Cryptic
3. Filter Feeding

The semi cryptic zone is the zone which occurs in the sections of the reef which are either deeper down the face or in naturally occurring overhangs in the reef structures. This zone has a very low light level and can only support photosynthetic organisms which can survive in this type of area.

The cryptic zone is the zone which occurs in the sections of the reef where light if any is far too weak to support any photosynthetic organisms in any way at all, and can only support non photosynthetic organisms. In the natural reef this occurs either within caves or deep into the overhangs of a reef structure.

The filter feeding zone is effectively a combination of the semi cryptic zone and the semi exposed zone. The difference in this mixed zone is that there is little light but very strong water currents, therefore particulate matter in the water can be delivered and consumed via the various filter feeding organisms. This zone is normally where the non photosynthetic soft corals occur.

Understanding the differences between the zones enables you to be able to see what zones you currently have in your aquarium – you will be surprised as to how many you actually have. You will probably find that you have many or even all of these types of zones in parts of your aquarium, however some may be quite small – e.g. small caves in the rock face.

You need to consider these types of zones when setting up a new reef system and also when introducing corals into the aquarium. When purchasing a new coral you need to understand the requirements of the coral and ensure that you have an area of the correct zone available in your aquarium to support it.

In your aquarium you will have various zones in various sizes, however one which is a valuable addition to the aquarium is the implementation of a designated cryptic zone.

A designated cryptic zone can easily be implemented into an existing system by adding a new aquarium into the system, possibly next to the sump, in the sump etc. This aquarium is filled with aquarium water via an overflow from the main aquarium or a tee off from an existing overflow. A small amount of substrate needs to be added. On top of this substrate is placed some pieces of live rock, sponges, sea squirts, non photosynthetic corals etc – effectively any non photosynthetic organism which can survive in a cryptic zone. The aquarium should then be effectively covered up to prevent any light from entering. Dirty water (un-skimmed as DOC’s are a requirement in this area) is fed to this aquarium at a very slow pace and there is minimal water current. This un-skimmed water is best fed into the cryptic zone along the top of the water. What this does is allow the particulate matter in the water to slowly settle down onto the organisms so that it can be consumed. The matter also falls onto the substrate. This allows for the growth of the organisms and therefore more removal of particulate matter from the water. Water from the cryptic zone normally overflows down to the sump so that it can be skimmed therefore for this reason you will need to install the cryptic zone aquarium higher than the sump so that it can overflow. It is also advisable to add some types of cleanup crew into the cryptic zone aquarium so that they can deal with any particulate matter on the substrate, rock work etc.

I have seen various designs of a designated cryptic zone in use. Some have even been combined with deep sand beds/plenums. Occasionally if you open up the covers and have a look you will be amazed at the life which is growing in there and how fast it grows. The thing I like about a cryptic zone is that sponges can quite easily grow. Sponges are a good filtration tool and utilising a cryptic zone will afford you the opportunity to grow some of them.

Of course more than one zone can be implemented whether this is directly in the display aquarium or by using external aquariums.

Whatever type of marine aquarium is kept, reef system or fish only system, there is one function that is totally essential. It isn’t a modern natural ‘invention’ either, it applied to those earlier aquarists just as much. The difference is that in the very early days the aquarists didn’t know anything about it. Before my time a pioneer marine aquarist thought he could keep his aquarium clean more easily by using what turned later into the much used under gravel-filter. I believe his name was Straughan. He was amazed about the length of time he was able to keep livestock, and put it down to better cleanliness. Investigations showed that in fact he had stumbled onto the secret of keeping any marine system basically healthy. In a way it was due to better cleanliness.

Livestock in an aquarium continue with their normal life functions. They are fed. Algae can die and rot as can uneaten food. This protein breaks down into a deadly toxin – ammonia. In the presence of not a great amount of ammonia livestock can be badly affected or die. Fish could hang quietly at the water surface, or swim in a very erratic manner, even upside down, or sit on the aquarium bottom leaning against a rock, and breathing could be rapid. This situation is very serious.

Yet in the modern aquarium the problem of toxins hardly arises, except perhaps in the case of a beginner who does not use patience and stocks too rapidly.

The saviours and the servants of the aquarist are bacteria. These bacteria break down toxins and the process is generally known as the nitrogen cycle.

Ammonia is very toxic and is broken down by bacteria called Nitrosomonas. The toxic ammonia is converted to nitrite, which is also toxic and nearly as bad as ammonia. That’s a lot of good! Well, another bacteria then comes into play and converts the nitrite into nitrate. These bacteria are called Nitrobacter. Nitrate can be bad at high levels, but is safe in comparison to ammonia and nitrite. The nitrogen cycle does not stop at this point, but continues when the nitrate is converted to nitrogen gas. The gas escapes from the aquarium and the cycle is complete.

Simple, nature saves the day!

Yes, it does, but there has to be a catch and here it is – the ammonia/nitrite conversion bacteria need a different environment to the nitrate bacteria.

The ammonia/nitrite bacteria require an environment that provides obviously ammonia and nitrite, and in addition they need a good supply of oxygen. This oxygen can only come from the water (except in one instance) so the aquarist has to provide plenty of water circulation to ensure good gas exchange at air/water interfaces such as the surface of the seawater. The home for the oxygen hungry bacteria can be in a canister filter and the like with suitable media. What is the exception mentioned – this is the so-called trickle filter. As the seawater running down is exposed to the air, oxygen is plentiful.

Providing a suitable home for the ammonia and nitrite bacteria is easy. The aquarist needs to ensure that the canister etc filters are properly matured, and this is achieved by using a prepared commercial maturation fluid. Using test kits, once the nitrite has disappeared the filter is initially mature. The instructions with the fluid will give details which are very straightforward. The nitrite showing as cleared means that there is a presence of bacteria which will deal with ammonia and nitrite. When the filter is initially mature, stocking can commence, but with great care and patience, as the filter is still unstable and needs to adjust to the bio load placed upon it.

The problem – here we go again – with canister etc filters is that the complete nitrogen cycle is not achieved. This is because they operate in an oxygen rich environment. Bacteria that deal with nitrate can live in an oxygen rich environment too, but under this circumstance they will not deal with the nitrate. An environment must be created where there is a lack of oxygen, and in this circumstance the bacteria will turn to the nitrate. The bacteria need oxygen, and the only way they can obtain it is to extract it from the nitrate, which breaks the nitrate down.

So there is no reason why a marine system cannot use a canister etc filter. It does mean though that the aquarist must keep a careful watch on nitrate levels as well as other parameters. Routine seawater changes will control nitrate to a degree, as will good husbandry such as a proper feeding discipline. There are other ways to control nitrates which will not be dealt with here.

There is a way of achieving the full nitrogen cycle, and that is to use live rock. This live rock (LR) can be used in fish only and reef aquariums. In the reef aquarium it has the secondary benefit of providing a material with which to construct the reef.

LR works as filtration because it is porous and provides a home for the bacteria. On the surface and inside toward the surface dwell the bacteria that use oxygen and deal with ammonia and nitrite. Deeper inside, where oxygen levels are depleted, dwell the bacteria that can only obtain oxygen from nitrate. Therefore the total nitrogen cycle is achievable. It is important that sufficient live rock of good quality is provided.

Using LR the aquarist still needs to monitor seawater parameters. Nitrate is included in those parameters, as LR has limits the same as anything else. That said, it is a wonderful filtration media.

Whatever type of bio filtration the aquarist uses, the bacteria will not make many demands, and the demands they do make are easily met. Fail to meet those demands, or pass the point where the bacteria do not have the capacity to deal with toxics, and the consequences could be very serious.

Provide suitable media and well oxygenated seawater, have patience with stocking and do not overstock, and nature’s bacteria will work silently and unseen providing life support.