What Salinity Should I Keep My Marine Aquarium At?

Marine aquarists use a hydrometer to measure the specific gravity (SG) of the seawater. The hobby hydrometer is not a pure scientific instrument but is capable of sufficient accuracy to enable stability of the SG – provided the aquarist does at least a weekly check.

Marine aquariums come in two main types, fish only and reef. To be precise, for ‘reef’ I should really say mixed reef and corals only reef, the former being corals and fish (the usual).

The first consideration is what SG is really necessary. To answer that it would seem best to look at the wild reefs, our livestock’s natural home. The SG of the sea in those locations should give the answer. Well, yes it should, but it doesn’t seem as simple as that. Is it ever!

The sea is considered to be stable which for the volume taken up is not really surprising. The SG on the reefs though is perhaps surprising, as it can range from 1.017 to 1.031*. Specific gravity is affected by temperature and some variance in temperature is understandable. In addition, some seas are more ‘land-locked’ than others such as the Red Sea. So there is going to be variance.

Some state that it is best to mimic nature and I sympathize with that. However, mimic which reading?

Looking at averages could be the answer. The lowest encountered salinities (on reefs measured) had an average of 1.025, and the highest 1.026*. Now this is more like it.

Provided livestock are acclimatized properly there is tolerance to some change which over a period becomes the normal. Generally, fish are like this and will happily live in seawater with an SG from 1.022 to 1.026. (Some aquarists use lower SG levels for specific purposes.) There seems little point in having a higher SG than necessary so many fish only systems run at SG 1.022. There is some evidence that certain parasites don’t do so well at 1.022 so that is a bonus. Also, and very much secondary, not so much dry salt will be required for routine seawater changes which will reduce costs a little.

What of the reef system? Whether this is corals only or mixed, the corals dictate the SG requirement. Corals are much less tolerant of a lower SG and 1.024 is the minimum for them. The range usually cited for corals is 1.024 to 1.026.

Whatever the seawater SG is, it should be stable. Testing at least once weekly is required and unlike many other types there will not be a need to renew a test kit from time to time. The hydrometer, barring accidents, is a once only purchase.

SG is a very important parameter of seawater and one that is very easily controlled. The SG could reduce because of salt ‘creep’, where salt encrusts overhead wiring, lights, glass and the like. The SG could increase because of poor seawater top-up management, as only fresh water evaporates leaving the salt behind. High quality seawater is the often quoted number one necessity and simple monitoring is required.

(*Reference: Aquarium Corals. Eric H. Borneham)

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The Constituents Of Seawater

The seas and oceans cover the majority of the planet surface. Within those seas the wild reefs have grown and all of their needs are met, be that calcium or whatever. The life on the wild reef has had a very long time to adapt to the sea, which is considered to be stable.

Some of these life forms end up in the home marine aquarium. With the natural seas being so stable it follows that for success the conditions on the wild reef should be duplicated as near as possible, and conditions provided that successfully permit life to function and be healthy.

Seawater quality is the number one on the list of ‘must haves’ for success so it follows that the seawater used should be as close as possible in make-up to the natural kind. In much earlier days aquarists would obtain some constituents – not all of them by any means – from a chemist and mix up a brew. Livestock existed in this fairly well for a while but trouble usually appeared. Nowadays there are many high quality dry salt mixes available which the manufacturers state equals the natural type. Be that as it may, the appearance of these dry salt mixes has brought the successful maintenance of a marine system within the reach of every aspiring aquarist provided the interest in the hobby is maintained and the requisite maintenance is done.

Seawater is a mix of many things, some of them present in major amounts, others in trace amounts, and more with a very tiny presence. So for the benefit of anyone interested there follows a list of the make-up of seawater. There is clearly no requirement of any kind for an aquarist to know them but as said it may be of interest. It could also be of use for aquarists who wish to maintain natural levels of important parts such as calcium etc.

Major Elements. (All measurements in mg/l)

Chlorine	18880
Sodium	10770
Magnesium	1290
Sulphur	884
Calcium	412.1
Potassium	399
Bromine	67.3
Carbon	28
Nitrogen	15
Strontium	7.9
Boron	4.5
Silicon	2
Fluorine	1.3

Trace Elements. (All measurements in ug/l)

Lithium	180
Rubidium	120
Iodine	60
Phosphorus	60
Molybdenum	10
Zinc	4.9
Argon	4.3
Arsenic	3.7
Uranium	3.2
Vanadium	2.5
Aluminium	2
Barium	2
Iron	2
Nickel	1.7
Titanium	1
Copper	0.5
Cesium	0.4
Chromium	0.3
Antimony	0.24
Manganese	0.2
Krypton	0.2
Selenium	0.2
Neon	0.12
Cadmium	0.1
Wolfram	0.1
Cobalt	0.05
Germanium	0.05
Xenon	0.05
Silver	0.04
Gallium	0.03
Lead	0.03
Zirconium	0.03
Bismuth	0.02
Mercury	0.02
Niobium	0.01
Thallium	0.01
Thorium	0.01
Tin	0.01
Hafnium	0.007
Helium	0.0068
Beryllium	0.0056
Gold	0.004
Rhenium	0.004
Lanthanum	0.003
Neodymium	0.003
Tantalum	0.003
Yttrium	0.0013
Cerium	0.001
Dysprosium	0.0009
Erbium	0.0008
Ytterbium	0.0008
Gadolinium	0.0007
Praseodymium	0.0006
Scandium	0.0006
Holmium	0.0002
Lutetium	0.0002
Thorium	0.0002
Indium	0.0001
Terbium	0.0001
Samarium	0.00005
Europium	0.00001
Radium	0. 00000007
Protactinium	0. 00000005
Radon	0. 000000000006

Constituents with a tiny presence.

Technetium

Ruthenium

Rhodium

Palladium

Osmium

Iridium

Platinum

Astatine

Francium

Actinium

(Reference: ‘Baensch Marine Atlas’. Helmut Debelius & Hans A. Baensch)

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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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The Necessity For Stability

There are some really stunning marine aquariums to be seen nowadays. Some of them are big, some are small and some are very small. In the big aquariums the beauty is probably mostly in the impact on the eye. In small and very small aquariums the beauty is probably more in the detail. They all have in common Mother Nature’s life forms in all their variety and colours.

There is something else that all successful marine aquariums have and that is environmental stability. This simply means that the different levels that are maintained with various items have little variation. Some of this is achieved automatically, some with the assistance of the aquarist.

There isn’t any intention of going into the full list of all the parameters that could be present as different systems – fish only and reef – vary. This is not to say that it doesn’t matter so much in one system or the other with parameter stability as it does. However, the reef aquarist needs to pay more attention to more parameters than one with a fish only system.

Some common examples won’t go amiss however. Temperature is important and the selected temperature should not vary unduly. This is commonly maintained by a heater/thermostat where the variation could be +/- 1 deg F. The seawater specific gravity should not vary measurably over a short period. The problem with seawater is it evaporates, or at least the water content does leaving the salt behind. Therefore the salt content has a tendency to rise and this is prevented by an auto top-up system or a manual top-up by the aquarist, the latter usually needed daily. The lighting and the lighting period may not seem like a parameter in the usual sense but stability is required with this also. With a reef system it is important that the spectrum and intensity are correct so bulb and/or tube changes are required periodically. Common to fish only and reef systems is the ‘lights on’ period. Whatever the individual aquarium requires, it should be regular and controlled by electric timers. This provides the livestock with a day and a night which they become used to. To enhance this, many aquarists include a ‘dawn and dusk’ cycle using the blue actinic fluorescents that are often fitted. These are set to come on ½ hour and go off ½ hour before and after the main lights turn off. As said there are more parameters, mainly to do with the seawater.

Stability is required because marine livestock could be said to be the spoilt children of Mother Nature. Disregarding the pollution and other damage caused by mankind, the wild reef is a stable environment. The reef is washed by the sea and oceans where volume is measured in cubic miles. The parameters of the seawater hardly change because the seas and oceans are so huge. There may be very short term changes in salinity at the surface during and for a short time after a heavy tropical rain storm and there may be some variations in temperature according to the time of day but overall stability rules. The life forms on the reef have adapted to this over a very long period indeed and they are hardly able to change quickly to a new environmental situation. That is why it is so important that new livestock are acclimatized properly to home seawater, which enables them to have at least some adaptation time. It is remarkable that livestock survive so well when they have faced the stresses of travel and an introduction to more than one holding tank on the way.

Compare the stable environment of a marine fish to that of a freshwater one in an ordinary small slow moving river. The freshwater fish is subject to more temperature change as the low water volume is more easily affected by the sun. If there is heavy rain then the water flow will increase and at the same time run-off into the river of soil will cause quality reduction of the water purity. In times of drought the river may reduce to a trickle and be even more subject to temperature and quality variation. Fresh water fish survive all these variations – in fact, the ability of different species of freshwater fish to survive extreme variations is remarkable. They have of course adapted to their environment in the same way as marine species have adapted to theirs.

The marine aquarium as said presents a lovely picture, usually fascinating to the non-aquarist as well. The beautiful and diverse livestock that could be present all depend on a high quality stable environment.

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Dosing Kalkwasser

Kalkwasser, otherwise known as limewater, is actually calcium hydroxide. Kalkwasser is a very fine powder and is normally introduced to the aquarium with the top-up water. There are realistically two methods to add kalkwasser to the aquarium, these are by a ‘kalk reactor/stirrer’ or by using what is called the drip method.

The drip method is where the kalkwasser is mixed with some prepared top-up water. It is important when mixing kalkwasser that it be mixed slowly, the reason for this is that it is imperative that as little air as possible gets into the top-up water. If too much air gets into the water then the kalkwasser will turn into calcium carbonate. Once the top-up water is prepared it should be left to sit for at least 2-3 hours so that any sediment can settle to the bottom of the container. The mixture which is left above the sediment is what will be introduced to the aquarium.

It is best to siphon this mixture out and dispose of the sediment. After the mixture has been siphoned out it is ready for use.

The kalk reactor/stirrer is where kalkwasser is introduced into a sealed chamber, within this chamber is a stirring device which mixes the kalkwasser and water. Water is pumped into the reactor normally by the use of a dosing/peristaltic pump and this water because of pressure forces water rich in kalkwasser into the aquarium.

Obviously the kalk reactor is easier than the manual method but both methods do work.

It is important when dosing kalkwasser not to dose it quickly. The reason is that water mixed with kalkwasser is of a very high pH. Therefore introducing it too quickly can alter the pH level of the aquarium water. To get round this problem you could either use a pH monitor to control the kalk reactor, or drip the mixture into the aquarium at a rate of about 1 drip per second (always drip into a high flow area). It is also worthwhile keeping an eye on the pH levels by testing the water using a pH water test kit.

There are both advantages and disadvantage in using kalkwasser in an aquarium. The disadvantages are twofold. One is that if you do not use a kalk reactor it takes time to mix the solution, the other is that because of the kalkwasser being added with the top up water you may not be able to introduce enough to maintain a steady level of calcium. The advantage, though, is that kalkwasser is very rich in calcium and can, if used correctly, maintain a high level.

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Dissolved Oxygen In Seawater

Don’t worry; we’re not going all scientific. There’s no need to anyway, the detail the marine aquarist needs to know is straightforward.

Oxygen is a very important dissolved gas in the seawater. The livestock need it to survive as we do – no oxygen, no life. If dissolved oxygen is in short supply then the aquarium livestock will be subject to stress, and if the oxygen level is continuously too low disease and maybe death will follow.

It isn’t just the livestock that will suffer either, the bacteria in the bio-filter will too. These bacteria operate the nitrogen cycle when ammonia is converted to nitrite which in turn is converted to nitrate. The ammonia and nitrite are toxins and will kill at quite low levels, so the bacteria’s welfare is paramount. The bacteria that convert the toxins are oxygen hungry and rely on the amount available in the seawater.

In addition if there is a good supply of dissolved oxygen in the seawater the redox potential will be reasonably high meaning a clean environment. For simplicity’s sake the redox potential is a measure of ‘cleanliness’.

Oxygen is taken into the seawater at air/water interfaces, the major one being the aquarium seawater surface with more in the sump, weirs, overflow pipes (where air is also in the pipe) etc. The intake of oxygen is dependent on efficient seawater movement, and without this movement trouble could follow.

There is about twenty times more oxygen in the air than there is in seawater. Seawater in the aquarium should have an oxygen level of between 6 and 8 ppm (parts per million). The average amount for a well designed reef aquarium is 6.5 ppm*. Not a lot really, but quite sufficient if all is operating properly. This amount of oxygen varies somewhat according to the salinity and temperature of the seawater – another reason why high temperatures bring the aquarist closer to the ‘edge’. Further, oxygen levels can fall at night when the aquarium is in darkness as, for example, algae do not photosynthesize. This can be combated by having algae in a sump which has an opposite lighting cycle, that is, the algae are lit when the main display lights are off.

All aquariums, be they coral only, fish and coral or fish only should have adequate circulation and seawater oxygen levels. However, it is the fully stocked fish only system with its higher numbers of fish that could be most at risk.

Fish place the highest demand for oxygen (I do not know the demand for oxygen placed by bacteria) so it follows that the more fish the heavier the oxygen demand. There are two dangers – first, the demand cannot be met because the aquarium is overstocked, and second demand cannot be met because oxygen intake in insufficient.

In the modern aquarium there are some devices that assist with oxygen such as the protein skimmer. Reliance should never be placed on these devices for the purpose of oxygen supply. If they fail there could be trouble. The seawater in the sump, if one is used, should not be counted into the system net gallonage when stocking is being considered so that those gallons assist with seawater quality including oxygen.

So consider a fish only system which is fully stocked and has been stocked correctly. If the system design is good there should not be any problem with oxygen as long as everything is running. Fresh oxygen is being taken in at the air/water interfaces all the time as more seawater reaches these surfaces and is then distributed around the system.

What if a circulation powerhead breaks down? The seawater movement is clearly going to reduce, though there may still be enough oxygen intake – or there may not. In the latter case, there isn’t any adjustment by the fish to economize on oxygen usage, so they will exist on the oxygen that is available. The demand will reduce the oxygen until it has reached critical levels, and the danger of suffocation arises. This of course will be made worse by the demands of the bacteria in the bio-filter. The same applies with a power cut when all circulation ceases. The reduction in the available oxygen could be more rapid and the danger of suffocation would arise more quickly.

It is clear that stocking is an area where great care needs to be taken. In the reef aquarium there is a smaller danger of oxygen problems as seawater quality is protected by having less fish though care still needs to be taken. In a fish only system with its heavier fish load, and not forgetting to consider the higher numbers of oxygen hungry bacteria there will be, the danger of oxygen depletion is higher.

The guidelines for stocking both reef and fish only systems are readily available and should not be exceeded. In addition, for peace of mind and especially in areas where power cuts are known to occur, the aquarist may wish to consider back-up battery operated powerheads, or even a small back-up generator with enough power to drive the aquarium circulation system and heaters.

No aquarist would wish to see the expensively furnished aquarium suffer or even die because of inconsiderate stocking or the event of power loss. The life in the aquarium deserves better than that.

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Oh, no, nitrate…

…and I don’t know why. I’ve live rock and everything seems fine at the moment, but I’m worried..

These words are quite understandable. Over and over again mention is made of seawater quality and how important it is – in fact seawater quality is the number one requirement, ahead of lighting (for a reef aquarium). So concerns in this direction are quite correct.

First, without being over scientific, what is nitrate? Every aquarium in order to be healthy needs a biological support system, commonly called a bio-filter, though some aquarists call it aquarium life support. This filter when functional is loaded with bacteria. The life processes of livestock and the rotting of uneaten food, algae and the like creates toxins, the first of which is ammonia. This is deadly to livestock. Bacteria within the bio-filter convert the ammonia to nitrite, again nitrite is a toxin and nearly as deadly as ammonia. Other bacteria then convert the nitrite to nitrate which in general is not toxic, but detrimental to seawater quality at too high a level. The bacteriological process has the overall title of ‘The Nitrogen Cycle.’ This cycle under certain conditions continues when nitrate is converted to gas which escapes from the aquarium, but here the concern is nitrate.

In the aquarium, whatever type it is, ammonia, nitrite and nitrate are being continually produced. The production is at its highest in a fish only system, as fish consume relatively large amounts of food which enters the Nitrogen Cycle process. Reef systems have lower fish loads, but nevertheless the same applies. The bacteria are continually hard at work.

The guideline that is given for nitrate when tests are being done is 10ppm (parts per million) or less in a reef system, and as close as possible in a fish only system. Why ‘as close as possible?’ It is more difficult to maintain a low nitrate presence in a fish only system because, as previously stated, there is a higher fish load and consequently heavier feeding. Why is the level stated more strictly for a reef system? This is because there are corals present and these are generally more sensitive to nitrate than fish. Note that some fish are more sensitive which should be noted in research before purchase.

Just to wander off the point a moment, there is something else that is interesting as well. I have never encountered this problem. A good while ago a well-known aquarist was asked in a magazine why a recently purchased fish, stated by authorities to be ‘reasonably hardy’, on introduction to a fish only system died. All the other fish present, some considered to be less hardy than the new addition, were fine. After a considerable amount of head scratching, it transpired that the nitrate reading in the seawater was approaching 150ppm. A little high in anyone’s book! There wasn’t any mention of problem algae which was fortunate for the aquarist. The fish that were already in the aquarium had been there from the word go or a little later. It was also discovered that seawater changes were done very spasmodically. So why did the new fish die? It had been purchased from a retailer whose seawater quality would have been at least reasonably good with low nitrate. The fish had then been introduced to very polluted seawater and had succumbed. What of the other fish? These had been in the aquarium for a long while and the nitrate level would have risen slowly. So they had become accustomed, or perhaps it is better to say ‘hardened’, to the nitrate presence. The advice was to carry out regular seawater changes and bring down the nitrate level, but not too quickly in case of any affect on the resident fish.

I bet that problem doesn’t happen very often. Anyway, back to the text.

There’s nitrate present – what to do? If the nitrate is within the guidelines, then perhaps it could be lowered even further by a small increase in the amount of seawater changed at routine changes. It is when it is quite high that is of most concern. The seawater needs to be of high quality and there isn’t any desire to tempt fate by providing nourishment for nuisance algae.

The first action is to attack the problem by, as just mentioned, increasing the amount of seawater changed. The basic general guideline for routine seawater changes is 10% of the net gallonage in the whole system but this can be flexed according to need. It is best not to increase the amount above 25% (severe cases) as the ‘raw’ seawater in this quantity isn’t always happily received by livestock. Increasing the amount changed increases dilution. The level should come down slowly until it is acceptable. The continuous addition of food and presence of livestock means that the Nitrogen Cycle is ever active (as it must be), so routine seawater changes should continue. After the following, if a cause of excessive nitrate is found the amount of the changes could be reduced again.

The above is treating the effect but what about the cause? It is best to start from square one and work through. There isn’t anything difficult in the process.

Excessive nitrate is in the seawater, but could it be getting in before any seawater enters the aquarium? First, have a look at the dry salt mix in use. It would be unusual with modern salts for there to be any nitrate (or phosphate) presence, but check that this is so by looking at the manufacturer’s information. Often the dry salt package will advise the salt is nitrate and phosphate free. In the unlikely event it isn’t free of these pollutants, change the brand to one that is.

The dry salt has obviously to be mixed with fresh water before use. It is highly recommended that RO (reverse osmosis) water is used, which is tap water that has been ‘super filtered’ to remove any unwanted substances. If RO water is in use, do a nitrate test to see if the unit is functioning properly. If there is a nitrate presence, then the heart of the RO unit, the membrane, may have a problem, and this should be checked. It may mean the purchase of a replacement unit.

If tap water is in use and not pre-filtered, then the same thing applies – test the water. In some areas tap water is fairly pure with a very low nitrate content, but in other areas it may not be. These areas are often agricultural where there is a lot of fertilizer in use (including nitrate), or industrial. If it is found that there is a nitrate presence, particularly a fairly high one, then it is best to invest in an RO unit and be rid of the problem. There isn’t much point in introducing nitrate when fresh seawater is mixed after the manufacturer has taken the trouble (which the aquarist pays for) to ensure the salt is nitrate free.

The next checks concern the aquarist’s husbandry disciplines. The aquarist can quite easily be over or under enthusiastic in some areas.

The first area to consider is feeding, where the majority of new aquarists overdo it. Overfeeding is fairly difficult to avoid by an experienced aquarist, as it is hard to ensure that all food goes where it is intended. The new aquarist is often over-anxious that the livestock get enough to eat and consequently too much food gets into the system, much of it is not eaten, it rots and joins the Nitrogen Cycle. This cycle as already stated produces nitrate. As a point of interest, as with nitrate, phosphate is linked to nuisance algae outbreaks. Guess how the majority of phosphate gets into the seawater – yes, with food. So it is very important not to overfeed. There are a few guidelines on feeding techniques to look at, including one under ‘Articles’ on this site titled ‘Food For Thought.’ Allowing a little time to learn how to feed and ensure the fish have enough, and at the same time avoid overfeeding as far as possible, is very worthwhile.

The second discipline that needs to be looked at is maintenance. Some aquarists like doing this (as some gardeners like weeding) and some do not. I don’t completely enjoy it, but do it willingly because the appearance of my reef, meaning the health and vitality of my livestock, depend on it. So how does maintenance have any effect on nitrate?

Good seawater circulation usually means good oxygen content. Oxygen is taken in at air/water interfaces, particularly the seawater surface in the aquarium. If circulation is at it should be oxygen content should be adequate. The bacteria that convert the toxins ammonia and nitrite are very reliant on oxygen availability in the seawater, so if there is plenty always available then the bacteria are able to function efficiently. This produces nitrate as previously mentioned. If live rock is used in the aquarium, and the oxygen loving bacteria are producing nitrate, then the nitrate converting bacteria convert it to gas, which easily escapes from the aquarium because of the good circulation. So the aquarist needs to ensure that circulation is adequate. Lack of good circulation could be a design error in a new aquarium, or in an established one the result of coral growth blocking seawater flow, or powerhead intakes being clogged with detritus, or tubes becoming narrow with detritus build-up. Checking these is part of ongoing maintenance. Intakes can easily be checked visually and the inside of tubes occasionally – seawater output, or the lack of it, could indicate tube blocking.

Detritus itself is a normal entrant to the aquarium. When maintenance is being done detritus should be removed as far as possible. This removal helps prevent rotting substances from entering the Nitrogen Cycle in the first place, thus not producing any additional nitrate. If detritus is heavy an investigation should be made to find out why and hopefully remove the cause. Seawater circulation usually means that detritus tends to settle in one or two particular areas, usually where the flow is lower. When a routine seawater change is done this detritus should be siphoned out.

Detritus can also settle like a dust on live rocks, or any rocks for that matter. It is a good idea to remove it once in a while. How can that be done? Obtain a baster (as used in a kitchen) or similar and gently pump seawater over the rocks. This will put the detritus in the seawater column and hopefully permit either a mechanical filter to extract it, or make it settle in an area where it can be siphoned out.

Another area to check is a sand bed. This sand bed could be in the display aquarium or in a sump, though in this case the sump is unlikely – unlikely because the sand bed here is one for decorative purposes only which would not normally be in a sump. The decorative bed is usually 1 to 2″ deep and made up of coarse coral sand. They can be very attractive. They can also get very dirty, as detritus settles into the sand bed between the grains. This is unwanted and the detritus should be removed by using, for example, a gravel cleaner on a reasonably regular basis – at least when the sand starts to look dirty. A dirty sand bed is not attractive anyway so the aquarist should notice it. (Note that only a decorative sand bed should be cleaned, not a DSB (deep sand bed))

Finally, nitrate can be produced in excess by the livestock, particularly fish. Not directly of course, but because of their life functions and the food that has to be offered. So it is important not to overstock – the more fish the stronger the pressure on seawater quality. More fish, more food and the harder the bacteria work. Normally they’ll do their job well, and normally they’ll work 24/7 on everything suitable and available.

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