First published in Aquarium World November 2007
A marine tank is a fascinating hobby which gives the owner not only the chance to keep some very colourful fish, but also the chance to grow living corals, have invertebrates such as crabs and shrimps, and if skillful enough, come close to recreating a little piece of coral reef ecosystem.
Even some of the amazing symbiotic relationships that happen between various species can be done in a reef tank, such as the clownfish and anemone combo. Anemones with clownfish living in them can be kept in a reef aquarium.
This is a beginners’ guide, the idea being to give a prospective reef tank keeper (reefer), an understanding of the basics. However there is much more to learn than this article, so then you are invited to start a thread in the FNZAS website forums with any more advanced questions, and questions specific to your own tank you are setting up.
This guide is divided into several sections with a basic explanation of each.
Water quality and filtration
Water chemistry & chemical additives
Putting it all together; How to construct a basic 1.2m (4ft) reef tank
This is going first because it is important to realize that setting up a reef tank properly is not cheap. To do a basic reef tank but do it right, you are looking at a minimum of $2,000 and upwards from there. In fact there are many reefers who have spent 10, 15, or $20,000 on their hobby. Here the confusion sets in because you will sometimes hear people claim they set up their tank for “500 bucks”. While this may in some cases be true, it will be because the person got some second hand equipment at a good price, or they set up the tank and it is in fact running, but down the track there will be problems because of el cheapo equipment. There is also the occasional person who breaks every rule and gets away with it. However over the years I have been saddened to see so many keen people start up, put so much time and love into their tank, but eventually fail because they could just not afford to buy the right equipment. It is important to understand up front what finance must be committed, rather than go through all the heartbreak of running something that is just not going to work, having livestock die, and eventually leaving the hobby disillusioned.
Water Quality and Filtration
Coral reefs in the wild grow where water is clear, clean, and pristine. In our tank we have to keep water to very high standards of cleanliness. Do this and success is virtually guaranteed. Don’t do it and failure is virtually guaranteed.
PROTEIN SKIMMER; Nearly all reef tanks use a protein skimmer. A protein skimmer removes small particles of dirt, bacteria, and whatever, from the water. The way it works is by pumping the tank water slowly through a vertical tube which has fine bubbles injected into it, either from an airstone, or of recent times, by more advanced and effective means such as air injected needlewheel pumps. The bubbles form froth at the top of the tube, and this froth collects dirt that has attached itself to the surface tension of the bubbles and risen to the top. As the froth builds up it overflows into a collection cup along with all the impurities it contains, and in this way a good quality skimmer will remove a high proportion of undesirable pollution from the tank.
LIVE ROCK; Virtually all reef tanks use live rock to facilitate bacterial reduction of the waste products that the skimmer didn’t get. Live rock is harvested from areas around coral reefs, and is made from old coral skeletons that have formed into chunks of rock. It is light and quite porous which provides an ideal living space for bacteria that eat waste products floating around in the water, and break it down to less harmful products.
NITROGEN CYCLE; This is a short explanation on how the bacteria in the live rock actually break down the waste. We add fish food to the tank, and all the various living organisms in the tank excrete waste, which if not removed would rapidly build up and kill everything. Nearly all organic waste becomes ammonia, which is highly toxic. However mature live rock contains bacteria that specialize in eating ammonia, and they turn it into nitrite. Then nitrite eating bacteria turn the nitrite into nitrate. Finally nitrate eating bacteria eat the nitrate and turn it into nitrogen gas, which leaves the tank through normal gas exchange at the surface of the water. In NZ, live rock is often purchased dry, and the bacteria are dead, or have formed spores. This live rock has to be “cured” which means left in water for a period of 6 weeks or longer, until all the various types of bacteria have established themselves and the rock can be used to provide filtration in a tank.
These are the two main essentials for good water filtration. Live rock, and a good quality protein skimmer. However here is a brief explanation of other things that can be used at the owners discretion.
Carbon is used to purify water, it can be purchased at a local pet shop (LFS) and is put in an area of high water movement. As water passes by it, waste gets absorbed into the pores in the carbon.
Other filtration media; There are other filtration media available from the LFS, that are used in the same way as carbon, but are designed to target something particular we want to get rid of, such as phosphate.
UV units are essentially a tube with a powerful UV light bulb inside. Tank water is pumped through the tube and the UV light breaks down complex organic waste into other forms that are more easily removed by the protein skimmer, or used by bacteria.
Canisters, hang on filters, trickle filters, and other highly aerated filtration types used in fresh water tanks, should NOT BE USED in marine tanks for biological filtration, although they can be used to hold carbon or similar. The reason is that nitrate reducing bacteria cannot function in a highly aerated environment, and use of these filters will result in a build up of nitrate to levels that are harmful to many reef dwelling creatures. In a marine tank use live rock to house the bacteria.
Deep within the pores of the rock, where there is less oxygen, the nitrate eating bacteria can do their job and keep nitrate levels low.
Phosphate really comes under the filtration section but because a good understanding of the topic is often critical to success or failure it is listed in its own section.
Phosphate is an essential component of living matter, and all living matter contains it. However in a reef tank it can often be the enemy as it can accumulate to unnaturally high levels and cause problems. Phosphate is in fish food, and every time fish food is added to the tank, some phosphate goes in. One way or another fish food eventually becomes waste and is removed from the tank by the nitrogen cycle. Phosphate though is not part of the nitrogen cycle and is left behind in the tank, slowly becoming more and more concentrated. Too much phosphate causes two main problems. One is that it precipitates onto calcium carbonate, which is what corals build their skeletons from. In this way it can slow, or even completely prevent, coral growth. The other problem is that phosphate is used by algae. If there is too much phosphate in a tank, this will act as fertiliser to algae, and the tank will turn green. On the other hand, even a green, algae ridden tank can be fixed, by removing the phosphate, and the algae will die.
So a very good part of filtration and water quality, is actually about phosphate control. There must be a means of “exporting” phosphate from the tank at least as fast as it is being added. One of these ways is the protein skimmer. The organic waste that the skimmer removes, will have a phosphate component. In a lightly stocked tank with a good quality skimmer, just the skimmer alone may be enough to keep phosphate at acceptable levels. In addition to this, regular vacuuming of the tank removes much waste that would eventually release phosphate if left. Also the amount of food being put into the tank should be looked at. Fish in the wild usually do not know where their next meal will come from, so given the opportunity will gorge themselves with all they can. This makes it tempting for the aquarium keeper to throw much more food in than they actually need. Often a new reefer will be surprised to discover they can cut the amount they are feeding in half with no detrimental effect on the fish at all. This will of course cut phosphate levels in half right there. However, often more measures to control phosphate are required. If phosphate is accumulating despite the skimmer and your best efforts at vacuuming, a phosphate absorbing media can be used. This is a resin of smallish particles that can be put in a bag and run in a canister or similar, or in a specialist phosphate reactor. In a green tank the effect of running phosphate removing resin can be dramatic, with algae turning white and dying within a few days. Or in bad cases it may take several weeks or months to get phosphate down to excellent levels where algae cannot survive. The presence of too much phosphate is often best judged by algae growing and/or less than clear water. Test kits can be less reliable. This is because some of the phosphate in a tank will be precipitated onto the substrate, some will already be within living organisms and algae if there is any, and only a tiny percentage might be in the water. So testing the water with a kit, will not indicate the total amount of phosphate in the tank, only the smallish percentage of it that is loose in the water. Phosphate tends to be taken out of the water by precipitation and grabbed by life forms, and only is in the water in large amounts if things are getting really bad. So a test kit may indicate you have no phosphate, when in reality the tank contains way too much. In general, if your test kit tells you there is any phosphate at all, you have too much.
Water Chemistry and Chemical Additives
Huge volumes can be written on water chemistry, so the following is basic information only, not an exhaustive study. There is much more, but this is what you HAVE to know.
The chemical parameters of most interest to reefers are salinity (salt concentration), which should be approximately 1.025. Then there is calcium around 400 mg/l, alkalinity around 7 – 11 dkh, and magnesium around 1250mg/l. PH also should ideally be around 8.3 although anything 8.0 – 8.5 is considered OK.
Salinity tends to slowly increase as water evaporates and concentrates the salt, so more fresh water has to be added to keep it at the right concentration of 1.025. Slightly higher or lower than this can be used. RODI filters (a very high standard water purifier) should be used to treat the fresh water you add to the tank.
Calcium and alkalinity are slowly removed from the water as corals use these to build their hard skeletons, and this has to be replaced. The three main methods to do this are firstly kalkawasser (lime water), which can be slowly dripped into the tank, or secondly 2 part additive which is a calcium mix, and an alkalinity mix, which are added separately but have to be in balance with each other. The third way is a calcium reactor, which is a tube that holds calcium carbonate rocks. Tank water is slowly pumped through, and carbon dioxide gas is injected which slowly dissolves the calcium carbonate into the water, thereby raising calcium and alkalinity levels in the tank. People wishing to use any of these methods can do further research on our FNZAS forum, and Google.
pH in a reef tank, is determined primarily by the amount of CO2 in the water, and the alkalinity. Provided the alkalinity (dkh) is at the correct level and there is sufficient aeration, pH will be at the right level.
Magnesium is needed at a level at least 3 times that of calcium, because without it the calcium quickly precipitates out of the water. So to maintain a calcium level at 400mg/l, you would want to keep magnesium at least at 3 times that, or at least 1200mg/l.
There are many other chemical parameters, and a host of additives for sale to dose them. However for the beginner, just keep salinity, calcium, alkalinity, and magnesium at the right levels, and you will do well. Beware the large amount of other additives for sale, it is very tempting to buy all sorts of expensive stuff to dose into our tank, but the benefit of a lot of them is questionable, regardless of how important the label may tell you it is. If tempted, ask on our forum.
Sands based on calcium carbonate tend to be the best for a reef aquarium in terms of the effect on water chemistry. These are sold in New Zealand as aragonite and calcite. As to grade, too small and it clogs and is hard to vacuum, and too big and food etc can easily disappear into it before the fish even eat it. A happy medium is a grain size around 2mm or so.
How much sand, and whether to have any at all, is a subject of much discussion in reefing circles. There are three main options. A deep sand bed (DSB), a shallow sand bed (SSB), or a bare tank bottom with no sand (BB).
DSB is defined as a sand bed at least 10cm thick. At this depth the bottom of it will be anaerobic (not much oxygen), which enables nitrate eating bacteria to operate, so a DSB can be an effective way to reduce nitrate levels in a tank. The other thing a DSB does is absorb a lot of muck and also phosphate from the rest of the tank. In the short term, this can be a good thing. But longer term the DSB can get so full it can become a source of pollution to the tank and cause the tank to “crash” (wipeout).
SSB is defined as 5cm deep or less. At this depth it will have little or no nitrate reducing properties, but on the other hand, is much easier to vacuum and keep clean.
BB is used by people wanting high water quality. With no sand at all, any dirt on the bottom is easily seen and available to be siphoned out of the tank.
Light is important because many of the organisms in a reef tank use photosynthesis, and without the correct amount and type of light, they will die.
Lighting is provided usually by either fluorescent tubes or metal halide lights. As a rough guide, allow 1 watt of light per litre of tank water as a minimum. Some corals are happy with this level of light, and others need more.
Light “colour” is measured in Kelvin (k). Bulbs of 10,000k give off the most proportion of light that is useable to the corals for photosynthesis. However 10,000k can appear a bit yellow and a tank with a more blue light makes the tank more attractive to look at. Therefore many people will add some bulbs higher up the spectrum at 20,000k, which contains a lot more blue (actinic) light. Or some people compromise and use bulbs at 14,000k, which can be OK for the corals and look attractive.
The ocean has a lot of water movement and corals are adapted to that and need it for cleansing themselves and other purposes. In our aquarium we have to imitate this, and put pumps in to move water around if we want our corals to do well. Basic rule of thumb is to have a minimum of 10 x’s water flow i.e., the volume of the tank should be pumped 10 times an hour. So for example, if a tank is 200 litres, we would want pumps equalling an output 10 times that, or 2000 litres per hour. 10 x’s flow is a minimum, some corals like a lot more than that, some aquaria use 50 x’s flow, and even 100 x’s flow is not unheard of.
To facilitate this there are special pumps available that clip to the side of the tank and pump large throughputs of water, specifically designed to produce large flow at zero head pressure. Some of them come with electronic control gear that can vary the flow to simulate wave action.
Water flow should not be blasting a coral from one direction only, ideally the flow should be chaotic, going one way, then the other. This is best achieved by placing a number of pumps around, pointing various directions and even at each other, so that the water is swirling and surging in the tank, corals love to be washed one way and another, and will respond well if water flow is set up correctly.
The other important function of water movement in a reef tank is to swirl the water around the live rock thereby enhancing bacterial filtration. The tank should have no dead spots, and the better the circulation is the better the water quality will tend to be.
Prior to purchase research should be done on each species of fish. Some will not get on with others and some need certain environments that your tank may not meet.
The great majority of fish for sale are wild caught and can come with a number of diseases. The use of a quarantine tank is a good idea, the fish can be kept in it for a few weeks to ensure it is not harbouring anything that could harm the rest of the fish in the tank. New fish sometimes have not yet learned to eat the kind of food we give them so a little research before purchase can help with useful information how to get the particular species settled in our system. Some fish are easy, and some don’t take to tank life easily.
This is what reefing is all about. The reef tank is really an underwater garden in which corals grow. They can be very beautiful and a well done reef tank can get gasps of amazement from anyone entering the room who has not seen it before.
There are hard and soft corals, the hard ones are the ones that build a hard skeleton, and the soft corals do not have a hard skeleton. The soft corals are generally more easy care, and a few of them can stand considerable abuse in terms of poor water quality.
The hard corals are divided into two broad categories, small polyp stoneys (sps), and large polyp stoneys (lps).
SPS are the branching type corals people normally think of when thinking of a coral. Their polyps are small, match head size or less. They can be very beautiful, but are the most demanding of good water conditions, correct lighting, etc. Growing healthy sps corals is often regarded as the pinnacle of achievement for a reefer.
LPS corals are demanding, but less so than sps corals. They like lower light and lower flow than sps, and some of them have brilliant colours. Their polyps are often around the size of the old 5 cent piece, but a few of them are much bigger.
For corals to do well a high standard of water quality is required, more so than is needed for fish. Observation of the corals, and making sure that their water quality needs are met, is the primary concern and as long as that is done the fish will be fine.
Nearly all corals for sale in New Zealand use photosynthesis. They do not photosynthesize themselves, but they have a symbiotic relationship with single celled algae type organisms called zooxanthellae, that live within the tissue of the coral, just under the surface. The zooxanthellae do the photosynthesis, and release the by products which supply the coral with nourishment. That, plus nutrients the coral absorbs from the water, can meet the feeding requirements of the great majority of corals. Some will do even better if we feed them directly but in most cases it is not essential. Feeding corals is a complex subject and it is best for the new reefer not to do this until gaining a reasonable understanding of the issues involved, or under the guidance of an experienced reefer.
Putting It All Together. How to Construct a Basic 4 Foot Reef Tank
There are many techniques and methods used to run a reef tank, and in advanced circles there is much debate over the finer points of which is best. However in the end they all boil down to a focus on keeping water pristine clean, and how to meet flow and lighting requirements of corals. The following is not the only way to build a reef tank, it is being offered as a guide to one way of building a successful tank.
Our tank will be around 270 litres, and will be on a stand. The stand will have inside it another tank, 2 1/2 feet long (75 cm). This smaller tank will be the sump. The reason for this is that marine tanks require some bulky, and perhaps, ugly equipment, such as for example a protein skimmer. In order to avoid cluttering up the main tank with this, a smaller tank, known as a sump, is often set up underneath, or near, the main tank, out of view. The main tank has one or more holes drilled in the glass, and an overflow is built, down which water flows from the main tank into the sump. The sump has a return pump, which pumps the water back into the tank. Ideally the pump will pump the volume of water in the main tank approximately 5 times per hour. The sump can incorporate all equipment including skimmer, calcium reactor, heater, chiller, top up and dosing set up, plus a bunch of others. The water flows from the main tank to the sump for filtration and other treatment, and is returned to the main tank, about 5 times per hour.
So now we have a tank on a stand, with a sump, and water circulating between the two. For water, we can either use artificial salt mix purchased from the lfs (local fish shop), that we mix with RODI filtered fresh water, or if we don’t want to buy salt mix we can use seawater collected when conditions are good and the water is clean. Seawater in New Zealand has a salinity around 1.028. The ideal for our tank is 1.025, so if using seawater we dilute it by around 10% with RODI water.
We now purchase a high quality needlewheel skimmer and put it in the sump. Also we put a heater in the sump, set to 25 degrees. Into the main tank we place some pumps to make water flow. We have decided to go for 20 x’s flow, so for our 270 litre tank, we put pumps in with a total output of 5,400 litres per hour. Water is now swirling around nicely. Now we are ready to put some rocks in the tank. We do not put any sand in yet. One kg of rock to each 10 litres of water is about the right amount, our tank is 270 litres, so we purchase from our lfs 27 kg of dried live rock. This live rock is currently not live, so we have to “cure” it. To do this we place it in the tank. The pores in the rock are full of dead organic matter and in a few days starts to rot. The water goes murky and when we test the water with our test kit, we discover ammonia. Our skimmer starts working overtime and we continually have to empty it. Gradually ammonia eating bacteria get established, and in around 2 weeks ammonia drops to zero. Now with our test kit we discover nitrite, which is what the ammonia eating bacteria make. We also find a lot of sandy looking dirt on the bottom of the tank. This is waste coming out of the rock, and should be siphoned. This is why we didn’t put sand in yet. In about another 4 weeks nitrite eating bacteria are getting established and nitrite levels start to drop. We now discover with our test kit that the water contains increasing amounts of nitrate, because the nitrite eating bacteria make nitrate. During all this time we do not use the lights so that algae cannot grow. When nitrite levels have dropped to zero, we can start slowly adding livestock to the tank. But first, the water is now rather polluted. We drain all the water and replace with nice new clean water. Wait a few days and test for ammonia and nitrite just to make sure both are still zero, and if so, we are ready to stock livestock. We still do not add any sand yet. So, ammonia and nitrite must be zero. Nitrate is less toxic and does not have to be zero. The nitrate eating bacteria take several months to kick in, so rather than wait, we start stocking.
Before adding livestock, we need some light. Nicely balanced lighting for a 4 foot tank can be done by 2 250 watt metal halides. This is giving 500 watts of light, nearly 2 watts per litre. It is enough that we can put high light needing corals on top of rocks near the lights, but it is not too much, so it will not burn lower light needing corals, which we put at the bottom of the tank. We use 14,000k bulbs, which gives a light pleasing to us the viewers, but still enough light that the corals need for photosynthesis. Once this is ready, we can stock fish and corals.
There are two sources of corals, the lfs, or from other reefers who may be prepared to give you prunings (known as frags) from their corals. Because different corals have different requirements for light and flow, and can live or die depending on being placed correctly in the tank, be sure to research each one properly and place it not just where it looks good, but where it will do well. If getting them from another reefer take the opportunity to find out what’s best for the coral from them.
For fish, we must stock slowly, over several weeks at least. The bacteria in the live rock have only just got established, and we do not want to overload them and risk another ammonia spike, which could kill everything. Some fish are territorial, and if you add them first, will claim the tank as “theirs”, and attack any fish you add later. To avoid this decide what fish you want first. Start adding the non aggressive ones and let them get established. Add the more aggressive ones last.
Now we have corals, we need to start making sure water chemistry is correct for them. If we have any “stoney” corals (corals that build a hard skeleton) we need to ensure calcium, alkalinity, and magnesium are correct. So we purchase some calcium chloride, some baking soda, and some magnesium chloride. These are mixed with water and dosed manually into the sump as required. A more detailed discussion of additives is beyond the scope of this article, however information is available elsewhere on the site about this. In time, most of us tire of dosing manually, and move either to a mechanized dosing system, or a calcium reactor.
In a few months we have a tank with corals and fish in it. There is still sandy type dirt appearing on the bottom of the tank from the rocks. We continue to siphon this out of the tank as needed, plus we do a 25% water change once a month. In time, the dirt shedding out of the rocks slows down, and we may now add sand if we wish. About this time algae will often start growing. It is important NOT to overstock the tank with fish. The more fish, the more we have to feed, the more phosphate, the more algae. We install a phosphate reactor in the sump. This deals to our algae problem plus has a beneficial effect on the tank in general. In time, the tank matures and stabilizes, and we find we can reduce, or stop altogether, use of the phosphate reactor. But if any algae starts to appear, we can turn it on.
Basic test kits needed are ammonia, nitrite, and nitrate. Also Calcium, alkalinity, and magnesium. Get salt water ones, not fresh water.
The other thing that is pretty much essential is an RODI water filter. This filters fresh water to a very high standard. In a marine tank we have to replace quite a bit of evaporation with fresh water. If we use tap water, or even filtered tap water, it contains phosphate. This phosphate will become more and more concentrated in the tank. The best way to avoid this is to use RODI filtered water. Many people fail to realize this and I have seen people leave the hobby because of the disappointment caused by problems caused to their tank by using non RODI water.
The above is ONE way to build a successful tank, but it is certainly not the ONLY way. There will be experienced reefers who do things differently to the above method. However the purpose of this how to build a tank section is to provide information that will enable someone following it, to build a reef tank that will be a success.
This article is in no way all the information that exists. It touches each subject only briefly, but at least you now know what the subjects are, and an idea of where to go from here. More information on all these topics is available on this site, and on Google. The best way of all if you definitely want to start a reef tank, is to contact someone who has one & see if they would let you have a look at it. Looking at the real thing while asking the owner questions can teach you much more in a shorter time.
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