The Essential Bacterial Service

There is one area in the aquarium no matter if it is fish only aquarium or a reef aquarium that the aquarist must have. If it is missing or inefficient there will be failure or trouble without doubt.

It is generally known as the bio-filter (bio = biological). Some aquarists prefer to name it ‘the life support system’ which is an apt description. Bio-filtration can be provided in more than one way though it all operates on the same principle. In addition the aquarist will be working with Mother Nature as it is bacteria that are relied upon.

Though it is commonly called bio-filtration as said, the bacterial activity that is occurring within the filter is nitrification and denitrification, under the overall heading ‘The Nitrogen Cycle’.

When livestock go through their life functions from day to day ammonia is produced, and ammonia is a deadly toxin. Fish produce the most. In addition rotting food leftovers and dead algae break down and produce more toxins. If there weren’t any bacteria then the fish would start to act strangely, swimming erratically and breathing heavily. Finally they would die, poisoned by the ammonia, so it is clear that the bio-filtration must be present and adequate.

One relevant point that can be made is that an efficient protein skimmer should be used. This is because the skimmer will remove dissolved organics from the seawater before the bio-filter needs to start work on it, thus reducing the work of the bacteria. A protein skimmer does not remove the need for a bio-filter.

How does The Nitrogen Cycle work? Toxic ammonia is the first problem, and bacteria (Nitrosomonas) are present in the bio-filter to deal with this. The ammonia is converted to nitrite.

Unfortunately nitrite is also a toxin, nearly as bad as ammonia, so bacteria (Nitrobacter) are again present to deal with it. The nitrite is converted into nitrate which is not considered toxic, though it is detrimental to livestock at a high level.

It is important that the seawater contains a high level of oxygen as the bacteria converting ammonia and nitrite are oxygen hungry. The term ‘nitrification’ covers the conversion of ammonia and nitrite.

The Nitrogen Cycle ends once the nitrate has been converted by bacteria into gas which escapes from the aquarium at air/water interfaces. This breakdown of nitrate is termed denitrification. The bacteria, in order to break down the nitrate, need a very low oxygen environment. This is because if oxygen were present the bacteria would use it and nitrate would not be reduced. Without an adequate oxygen presence the bacteria extract their oxygen needs from the nitrate, thus breaking it down.

So overall The Nitrogen Cycle is the conversion of ammonia to nitrite, and nitrite to nitrate. Then follows the conversion of nitrate to gas.

Giving the bacteria a home in the aquarium so that they can efficiently carry out their work is easy. First, the design of the aquarium should allow for optimum gas exchange which will permit high oxygen levels in the seawater. Next the media for the bacteria can be considered.

Nowadays the number one recommendation for bio-filtration is live rock. This is so called because the rock naturally harbours the needed bacteria, all of them, those that convert ammonia, nitrite and nitrate. The first two are near or at the surface of the rock, and the third deeper inside where oxygen is not plentiful. It is an excellent medium and in addition provides the aquarist with a natural aquascaping material for a captive reef or in a fish only system. Rock quality must be good and there must be sufficient to meet the demand of the livestock. Live rock is expensive because of the weight which is unfortunate, but nevertheless it should be a first consideration.

If live rock is not used, there are other methods. Probably the easiest is the canister filter, as a huge area of filter media can be provided and setting it up is straightforward. It is important to ensure that the amount of media can cope with the livestock present, so reference to the manufacturer’s recommendations should be made. The media when obtained will be ‘dead’, without any bacteria present. Bacteria are easily introduced by using one of the commercially produced ‘inoculation’ fluids which are easily obtainable. The information supplied should be carefully followed and tests made as instructed.

There is a shortfall with canister filters and similar devices in that the seawater being pumped through the media is oxygen rich. This is excellent for the bacteria that convert ammonia and nitrite, but nitrate will not be touched. Therefore there will be a slow build-up of nitrate in the seawater. I used the word ‘shortfall’ not ‘problem’ as it is easily dealt with. If the aquarist carries out routine seawater changes then the nitrate presence will be continually diluted and should be kept down to reasonable levels. 10% of the system net gallonage is the guideline for initial changes but if necessary this can be increased up to around a limit of 25%. If this is not sufficient to control nitrate then there is something amiss – the system is overloaded with livestock, or the aquarist is overfeeding and the like. There are ways to reduce nitrate by filtration using bacteria (the denitrator filter) but this will not be gone into here. There are other ways too but again they will not be gone into here.

The aim of every aquarist is to own a successful aquarium. There is equipment available to make this more possible. However, at the very heart of the system are the bacteria, essential to every system of whatever type, big or small.

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Seawater In The Aquarium

Seawater is very important in the marine aquarium – not a big surprise really! It needs to be of high quality and kept that way.

There is an article titled as above on the Marine Depot website. It was supplied to Marine Depot by Aquarists Online and I thought I’d bring it to your attention as it should be of interest to anyone, particularly relatively new aquarists. The article deals with many aspects of seawater and what can happen to it as it ages. There are a good few positive comments about the article from readers.

The link is below. While on the website why not have a look around.

http://kb.marinedepot.com/article.aspx?id=10686&query=Seawater+in+the+Aquarium

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How To Set Up An Aquarium For A Seahorse

These lovely and strange life forms are very endearing and become a household pet very easily. Children in particular seem to be fascinated by them.

The care of seahorses is not to be undertaken lightly. They need very similar maintenance to a fish only marine system, so the requirement to carry out maintenance regularly needs to be accepted.

Seawater will need to be mixed and the preferred pH range is 8.0 to 8.3 and SG (specific gravity) is 1.021 to 1.024. Temperature should be in the range 75 to 78 deg F (obviously this is for tropical species). As with all system types the seawater quality needs to be high – the ammonia and nitrite readings need to be nil, and nitrate should be 10 ppm (parts per million) or less. It is also necessary to carry out regular routine seawater changes, the guideline amount being 10% of the net aquarium gallonage as with other system types.

Unlike the fish only and reef systems, seawater movement should not be vigorous. There should be movement though and this can be created by powerheads in the normal way. They will of course have lower outputs. To judge the power of the current consider a field of corn. In a gentle breeze the corn will stir and sway a little but will be nowhere near thrashing about. The requirement for low strength currents is because the seahorse is not a strong swimmer.

Again as with all aquarium systems, seahorses need a bio-filter for their well being. This could be live rock, or a canister filter will suffice. If live rock is used it is best to try and ensure there aren’t any sharp edges that the seahorses could damage themselves on. Whichever type of bio-filtration is selected, it must be mature. Seahorses cannot be introduced until there is a mature bio-filter.

Unlike say surgeon fishes, seahorses do not demand a lot of space, they move about calmly and serenely. They should not be crowded of course. This means that the aquarium need not be large. For example, a 3ft by 1.5ft by 1.5ft aquarium would not be overcrowded with five seahorses (remembering that some are small and some much larger).

Decorating the aquarium is straightforward. There isn’t any need for a reef structure, but a few rocks (without damaging edges) could be used. These, as said, could be live rock, sufficient to ensure good bio-filtration. A decorative sand bed could also be used if desired, but it must be remembered that the bed needs to be cleaned periodically if necessary to ensure it is healthy. Sand traps detritus and could become dirty fairly quickly.

Lighting the aquarium does not present any problems as, like fish, the seahorses simply need to see and be seen. Generally, two fluorescent tubes should suffice, and a ‘dawn/dusk’ cycle could be introduced by using an electric timer. This will move the system a little closer to the natural sequence, as livestock should not be plunged into darkness or suddenly bathed in light. If algae are to be used (see below) then the lighting should take account of this.

Seahorses use their tails to hold themselves in any particular place, so it is necessary to provide them with anchor points. Some aquarists use artificial plants which can be anchored down, ensuring that the plants are constructed of soft plastic. Others use real plants and this is better. In this case ‘plants’ means the machro algae Caulerpa. This alga is decorative and reasonably easy to grow, some types being easier than others. It should sway in the seawater currents and when there is plenty of it looks very attractive. The alga has another purpose too, as when established it requires nutrients and these include phosphate and nitrate, two that the aquarist doesn’t desire. Caulerpa can grow vigorously and it should be harvested from time to time, always leaving enough for the seahorses and to ensure the algae stock continues to grow.

Feeding seahorses could be a problem as they are sometimes finicky and ignore the aquarist’s usual offerings of dead material. Flake food is a waste of time, the usual food being brine shrimp and mysis shrimp. If the seahorses refuse the de-frosted varieties then they will need to be started on live brine shrimp. These can sometimes be purchased from the local fish shop (LFS) or the aquarist can rear them himself. There are rearing kits available that provide all that is required and it is not a difficult job by any means.

Seahorses will take de-frosted shrimp often, however, and if this is the case it is best to use ‘enriched’ varieties as well as more than one type. Rather than putting a great deal of food in the aquarium, which will put pressure on the seawater quality, the aquarist could target feed, dropping food close to the seahorse’s current location. The low seawater circulation will not hinder this practice too much.

The fact that seahorses are being kept and there is low seawater circulation does not mean that nothing else can be kept in the aquarium. The aquarist could keep pipefish that also require the same environment. In addition there are snails and various other life forms that will not be detrimental.

If the aquarist sets the aquarium up with care, and provides a stable and high quality environment, then he or she should have an aquarium that will provide many hours of fascination. It is likely that children will want to be involved which is good. It could even be that the aquarist is presented with new additions to the aquarium in the form of many baby seahorses, born unusually from the father.

I have noted below a website from where an interested aquarist can extract much additional information.

http://www.seahorse.org/library/articles/SeahorseFactsAndInfo.shtml

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The Fluidized Bio-Filter

Bio-filters in marine aquariums are of enormous importance. Without the nitrogen cycle that is provided by Nature all aquarists would soon be in trouble. All those bacteria working away so industriously are doing us all a favour.

Bio-filtration, or the life support system as some aquarists call it, comes in several guises. The current best is live rock, whether that is aqua cultured or from the ocean. The rock from the ocean offers the possibility of a greater diversity of life in addition to the desired bacteria, but this includes of course unwanted life, such as certain crabs and shrimps, not to mention aiptasia anemones (now aren’t they just every aquarist’s favourites!).

Then there is the canister filter, a device that has been in use for many, many years. They are much improved nowadays with much easier access, meaning that most have got rid of those fiddly little clips that used to be used to keep the lid on. Most come with removable chambers thus making the insertion of media for mechanical, bio or chemical filtration easy. The canister is really well proven and highly reliable. Though not often thought of this way, they really operate a ‘closed loop’ when connected.

There is a further piece of equipment that isflui designed for bio-filtration, but it is not so well known. This is the fluidized bio-filter. Basically the device is a tube usually constructed of acrylic, with an inlet at the bottom and an outlet at the top. Inside is a quantity of sand – not just any sand but a type that resists wear in the tumble action it has to endure. A pump or powerhead is connected to the bottom inlet and the outlet at the top is fed back to the aquarium, usually at the opposite end. Sometimes the device is supplied with an inlet filter to help keep the sand clean, but if not it is easy enough to put a foam filter on the pump or powerhead.

As the seawater is pumped through the sand, the sand is ‘fluidized’. This means that the flow of seawater pushes the sand upwards with enough force to keep it loose, but not enough force to make it hurl about the tube. The result is that each grain of sand presents all of its area for colonization by bacteria. Such is the area that a fairly small unit can deal with a fairly large aquarium. Of course this also depends on the bio-load – a fish only system usually presents a larger load than a reef system.

The downside of this type of bio-filtration is that the nitrogen cycle will operate very efficiently, the bacteria converting ammonia to nitrite, then nitrite to nitrate, but it stops there. So nitrate will slowly build up in the seawater degrading its quality. This also applies to a canister filter.

The fluidized bio-filter is a perfectly viable alternative when a system is being considered. The units are usually ‘hang-on’ and easily fitted. The sand in the tube tends to degrade over a long period and the manufacturer often puts in a small bag for replacement purposes. The manufacturer will also advise the flow rate that is required to fluidize the sand correctly.

It is important that the aquarist maintains good general seawater circulation in the display aquarium as the bacteria that inhabit this type of device depend on the seawater’s oxygen content, in the same way as a canister filter and live rock. Also, in addition to the other benefits, routine seawater changes are required to control any nitrate build up.

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You Need To Have Enough Filtration In Your Aquarium

A successful marine aquarium is a wonderful sight. It doesn’t matter whether it is a fish only, coral only, or fish and coral system, there are certain items that need to be up to the job.

The first essential requirement is seawater quality, closely followed – at least in a coral only or coral and fish aquarium – by lighting. It is the need for seawater quality that makes filtration so important.

There are basically two types of aquarium filtration, excluding protein skimming which is often counted as such. The first is mechanical/chemical filtration and the second biological.

Mechanical filtration is where media removes sediment from the seawater by trapping it in suitable media. This is often done by using a canister filter which needs to be cleaned regularly and the media changed if it is showing signs of wear or failure. Mechanical filtration is not an absolute requirement and many aquarists do not use it. It is usually only necessary when there is a fair amount of sediment floating around in the seawater. Before employing a mechanical filter, it is best for the aquarist to ascertain why there is sediment and try to correct the problem.

Chemical filtration is also often done by using a canister filter and can be in conjunction with a mechanical stage – if so the mechanical stage normally comes first. Chemical filtration covers activated carbon, phosphate removing media etc. Again it is not mandatory to use this type of filtration, though some aquarists use activated carbon to supplement the protein skimmer and others run an anti-phosphate media continuously (phosphate is a nuisance algae nutrient and is mainly introduced with food).

By far the most important filtration is biological, and this applies to any type of system. The filtration carries out the ‘Nitrogen Cycle’, which is something all aquarists should clearly understand. Livestock introduce a toxin into the seawater, namely ammonia. This toxin is deadly to life forms in low concentrations but fortunately Nature has the solution. The biological media provides a home for bacteria in their millions, and the first group of bacteria convert the toxic ammonia into nitrite. Unfortunately nitrite is also a toxin and very nearly as bad as ammonia. However, a second group of bacteria convert the nitrite into nitrate, which, though problematical in a high enough concentration, is not generally harmful. If the Nitrogen Cycle is able to run the full course the nitrate is converted to gas which escapes the seawater.

There are one or two points that need to be remembered about the bacteria that provide this essential service. The first is that the bacteria that convert ammonia and nitrite are oxygen hungry, and to ensure their proper function it is necessary to provide seawater rich in oxygen by having adequate seawater circulation and air/water interfaces.

The bacteria that are able to convert nitrate to gas are not the same. They would use oxygen if it was available, but if it is not they take the required oxygen from the nitrate, thus breaking it down. Therefore the bacteria need to be in a very low or no oxygen environment to ensure that the required function is performed.

If for example a canister filter is being used for biological filtration the media is constantly exposed to oxygen. Therefore the breakdown of ammonia and nitrite will occur but nitrate conversion will not. Nitrate will remain in the seawater and will increase unless other adequate measures are taken.

If the biological filtration is by good quality live rock, then the full Nitrogen Cycle, that is ammonia-nitrite-nitrate-gas, should occur. This is because the oxygen loving bacteria accumulate near to the surfaces of the rock, and the bacterial nitrate converters are deep inside where oxygen is depleted.

Having considered all of this, it is clear that there needs to be adequate filtration material to accomplish the biological task. For example, a fish only system can employ live rock. Fish are producers of ammonia, much more so than corals, and an adequate amount of good quality live rock is needed to process the toxins. The live rock amount would need to be increased if the fish numbers were high as obviously there would be more toxins produced. As a general guideline 1½lbs of good live rock is considered necessary for each gallon in the complete system. So if there is a sump, count that in. There is a problem with the ‘weight system’ as live rock can be of differing weights, therefore when purchasing seek advice.

Similarly, when using a canister filter (or similar) for bio-filtration it is important to ensure two things – first that the canister can contain sufficient bio-media for the intended load and second that the flow rate through the filter is adequate. Manufacturers will advise the recommended aquarium size for canister filters, and media manufacturers will advise the suggested bio-loads.

Mechanical/chemical filtration is not so essential, so reading the media manufacturer’s recommendations is sufficient, if these types of filtration are required at all.

Stocking a marine aquarium without an adequate amount of bio-filtration will soon become obvious to the aquarist – sickly livestock and quite likely losses. Inadequate bio-filtration is likely to hit fish systems the most as they produce most toxin with their life functions. However, all systems require adequate bio-filtration, Nature’s free and essential service.

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First Introduction – Fish Or Invertebrate

The majority of aquarists decide that the first introduction to their aquariums should be a fish yet does it need to be this way.

I fully understand why this happens and perhaps this is due to historic reasons where aquarists used hardy fish to assist in the cycling of their aquariums. Something which I am glad to say is not done anymore. Perhaps it is the movement and colour of the fish which draws the eye. There are many reasons as to why people choose a fish as the first inhabitant of their aquarium. It uis of course not up to me to sway their decision in any way but perhaps people believe that a fish has to be the first introduction.

On another note if the aquarium is a fish only aquarium then the aquarists will of course be introducing a fish first!

For the aquarist with a reef aquarium however there is another choice especially when live rock is used as the filtration but it does not matter what filtration is employed. Live rock even when matured correctly is not very sterile and therefore may carry opportunistic parasites. When a fish is caught in the dealers it is put under immense stress due to the catching, the bagging, the transport etc. When the fish is introduced to the aquarium its immune system may be lower than normal and in a reef tank filtered via live rock it may become prey to opportunistic parasites.

I appreciate that the above can happen at any time in the aquariums life however at the very start the aquarist is learning and if a fish is lost at the very start then this is sad for obvious reasons however the aquarist’s confidence in the aquarium and his/her own abilities and may give up the hobby.
There are certain fish which are more resilient than others however a lot of these fish – damselfish for example can become problematic later due to the aggressive nature and it is very hard to remove a fish from an aquarium with live rock in it!

Another method at the very start instead of fish is introducing hardy invertebrates.

By introducing hardy invertebrates first the aquarist will gain experience in acclimatisation techniques as well as stocking techniques. At the very start when the aquarist’s knowledge is low for want of a better word it is probably fair to say that a fair amount of tinkering will be employed. What I mean by this is that the aquarists hands will be in the aquarium a lot moving various corals around as well as the relevant water movement devices until they are satisfied that the conditions provided in the aquarium are suitable for the aquarium inhabitants.

If the decision is made to introduce invertebrates prior to fish then the aquarium, as with fish must be ready for the introduction of them. By this I mean that the nitrogen cycle has completed, there are no large algae outbreaks evident or they are under control and the water conditions are maintained in accordance with the recommended levels. For examples nitrates should be low as should phosphate levels. More than that the water conditions should not just be maintained they should be stable.

With the aquarist deciding to introduce invertebrates in the first instance the equipment purchased and installed should be capable of support the life in the aquarium. For example the lighting needs to be correct. This may sound basic but I hear of a lot of people trying to keep corals under lighting which to be honest is just not suitable for them.

At this point – actually a lot earlier the aquarist should know what corals, fish etc that they want to keep and should have based their purchases around this decision. At this point in the aquariums life you would not be looking at introducing an SPS coral like acropora etc as the aquarium is simply not ready for it.

At this point the corals you will be interested in purchasing are the ones which are not too expensive and do not have the colour of the majority of SPS corals. This is not to say that these corals are dull and colourless as they are far from it but when you compare prices you will see what I mean!

Speaking of purchase again I recommend that you build a relationship with a local dealer, another hobbyist or an online area (like Aquarists Online hint hint…) where you can go and ask advice as to what is suitable etc. Building a relationship with others is important as you can use their experience, their knowledge to your advantage o=plus you can learn a lot about the hobby and will hopefully not make expensive mistakes.

When selecting corals you are looking for corals which are suitable for the beginner. When looking you will probably see some exceptionally colourful species. I would probably stay away from these as there are some species which do not contain zooanthellae and require feeding for them to thrive. A good example of this is the sun coral. There are also other colourful ones which are probably for more advanced aquarists or aquarists who have had stable aquariums for a long period of time.

You have to remember that the aquarium is new and the water, rockwork, sand, glass, equipment etc all needs to age. You can always come back to these more colourful corals when your confidence has grown by maintaining a reef aquarium for a number of years.

In my opinion the list below details what I believe to be good ‘starter corals’ and are suitable for first introduction.

• Button Polyps
• Xenia
• Mushrooms
• Leather Corals
• Star Polyps

This does not mean that you should not introduce fish. I personally think that an aquarium with just corals in and no fish lacks movement however I think that perhaps more aquarists should introduce invertebrates prior to introducing fish to gain both confidence in themselves as well as giving the aquarium time to settle.

This of course also does not mean that you will not get problems when introducing fish at a later stage. You might but just remember to acclimatise them properly and use a quarantine tank.

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How Fast Should You Stock The Aquarium

Throughout the years lots has been written about the stocking rates in saltwater aquariums – some of this information has been very informative and unfortunately some has been very misleading.

Misleading information provided has been along the lines of ‘1 cm of fish for every 5 litres of water’, ‘1 cm of fish for every 13 litres of water’ etc.

As you can see just from the above two examples it can be very misleading!

On top of the above there has been limited differentiation between fish only aquariums, coral only aquariums and mixed reef aquariums!

The main trouble is when it comes to stocking the aquarium – each aquarium is different. Each aquarium has different equipment, different animals etc. Even if you have two aquariums with exactly the same equipment then they would still be variances.

Overstocking in an aquarium is unfortunately something that the majority of aquarists do. For a long time they get away with it until something changes and the aquarium starts to go downhill. Basically if the correct care and maintenance is performed on a weekly basis and no equipment fails then some aquarists may be able to get away with overstock – until some area of the care and maintenance is missed, a piece of equipment fails and then the trouble starts.

The issue is not just with the aquarium being overstocked. Another issue is when the aquarium is stocked too quickly. This could either be that fish are introduced into the aquarium prior to the aquarium finishing its cycle, too many fish are introduced at the same time or not enough time is left in between the introduction of fish.

The first thing that the aquarist needs to ensure is that the aquarium is ready for the introduction of fish. By this I mean that the filtration in the aquarium is ready to process the waste created by the fish, uneaten food etc. This, as already mentioned is the cycle. In the cycle Ammonia is converted to Nitrite which is in turn converted to Nitrate. Both Ammonia and Nitrite are toxic to fish therefore no readings of these should be evident in the system.

At first testing only for ammonia will suffice, then testing for nitrite. When the ammonia levels reduce the nitrite should increase which should then reduce only for the nitrate to increase.

Nitrate is not toxic to fish but should be controlled either by water changes, natural methods etc to ensure that it stays within the recommended parameters for the type of aquarium you keep.

Once you have no readings at all for ammonia or nitrite then the aquarium is ready for the introduction of a fish – just the one don’t get greedy and overdo it. I appreciate that this is hard as there will be lots of beautiful fish in the shop which you could walk out with but you need to resist the temptation.

Before you go out to the shop though you need to realistically have a think about what fish you are hoping to keep in the aquarium (as well as corals and invertebrates if you are hoping to keep these). When you are thinking about this consider talking to more experienced aquarists or a couple of aquarium shops who you have started to build a bit of trust with. In my opinion it is good to build a good relationship with your local fish shop as they will get to know both yourself and your aquarium and you never know when you may need them.

When thinking about your list what you want to ensure is that all the fish you hope to keep will live happily with each other (and corals/invertebrates if you are keeping them).

There is something else you need to think about at this point – the hardiness of the first fish.

It is recommended that a hardy fish be introduced first into the aquarium at the start of its life. In my opinion this is correct as everything in the aquarium is new and basically the water is raw and too clean. A hardy fish is good but what you do not want is a territorial fish. A good example of this is the damsel fish. Whilst the fish is hardy it will quickly believe that the entire aquarium is its territory and when you introduce other fish into the aquarium they could easily get bullied which in turn leads to stress, disease and possibly death.

What you are looking for is a fish which is hardy yet is not territorial.

A good example of this is the common clownfish – tank bred if possible.

So let’s pretend at this point that you have gone to your local fish shop and ignored all the other fantastic fish and purchased just the one – a common clownfish.

Well done to you!

Now you have it home and you need to follow the correct acclimatisation procedures. A lot of people ask me if they need to quarantine their first fish. In my opinion there is no need to do this as there is nothing else in the aquarium which could be effected if this one becomes sick but if you are on the cautious side then quarantine the fish for a week – it won’t do any harm.

One the fish has been acclimatised to your aquarium it should soon start to explore, take food and perhaps even become bold.

At this point you may become tempted to go out and purchase one, two, three etc more fish. You should not do that though. You need to test the water. Prior to adding the first fish to the aquarium the filtration had nothing to deal with other than the cycle and any areas of die off which may have occurred. Now that a fish is in the aquarium you will be feeding it and not all that will be eaten and will fall to the bottom. What is eaten will eventually pass out of the other end and needs to be dealt with.

All this is processed by the filtration and the filtration needs time for the bacteria levels to increase. This is what you are waiting for – stability in the filtration.

This can again be done by testing for nitrite and nitrate. Even if these readings are zero for nitrite I would still wait a couple of weeks prior to adding a new fish. Give the aquarium time to settle and enjoy your new fish.

Once your readings are ok and at least a couple of weeks have passed then you can go and get another fish if you want to. Basically at this point you do the same again. Test the water and wait for stability.

Basically you should stock the aquarium very slowly. The quicker you stock it the more load you are putting on the filtration system and it may not cope. That in turn will mean that you may get ammonia or nitrite readings which are not good and as said are toxic to fish.

Also don’t forget that the faster you stock the aquarium the quicker it will get full. Enjoy stocking it and take your time.

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