Stocking The Saltwater Aquarium Part 2

In Part 1 stocking a fish only aquarium was considered. This time the reef aquarium will be looked at. Whatever the type of salt water aquarium, fish only or reef, water quality is important. In the reef aquarium, water quality needs to be excellent. Again, it is assumed that the aquarium is fully set up with suitable equipment, and the biological filtration (probably a ‘live’ rock reef with maybe a sump containing further filtration) is settled and adequate.

Why should water quality be more important in a reef aquarium? In the fish only system, consideration is given mainly to SG (specific gravity), pH, nitrate, and phosphate. (More, of course, if the aquarist is keen enough.) The same considerations apply to the reef, where the nitrate and phosphate levels need to be very low. In addition a routine check needs to be kept on calcium, magnesium, alkalinity etc. So, a few more parameters to monitor. The point of all this chatter with regard to stocking is that nothing should be done that will put excessive pressure on the system which could bring water quality down.

The first requirement for the aquarist is to decide what type of corals he/she wishes to keep. The coral type referred to here is soft or hard. Hopefully, this decision will have already been made, as the aquarist will have possibly installed the lighting to suit. It is not recommended that soft and hard corals are mixed, at least not at first until experience has been gained. Soft corals can release substances into the seawater that inhibit the growth of hard corals. Now it is into research, in books and on the internet. Whether soft or hard, the aquarist should avoid those corals that are marked as difficult until, at the very least, he/she has considerable experience. (The soft coral enthusiast should not fall into the trap of thinking that ‘soft corals are easy’. Many are comparatively hardy, but some are very difficult to keep.) During the research, note the expected growth rate of the corals if possible.

Once a choice of corals has been made, hard or soft, it is a good idea to go to the local retail shops (the more the better) to have a look at the corals in reality. It is likely with soft corals that most of the hardy species will be available, and the popular hard corals likewise. Now is the time to note down prices, look at colours, and growth types (eg branching, plating etc). Nothing will be bought yet.

Back at home, using a plan drawing (a simple rough one will do as long as dimensions are usable), place the desired corals as required. Pay attention to the need of each coral for light and water flow (obtained from research). Remember, the corals will grow, and if they approach one another with this growth the more likely a struggle for territory will develop. The plan needs enough corals to make the reef look properly ‘reefy’. Once the corals have been placed on the drawing, go back to the notes of prices obtained from the shop(s). There are corals available on the internet from reputable sources where prices might be somewhat better. Maybe there is an aquarist nearby who can help out. Maybe there is an aquarist’s club. There isn’t any need to fully stock with corals immediately, it can be done gradually.

There are many corals, soft and hard, that are being grown from ‘frags’ (cuttings) nowadays. This is being done by commercial organisations and also by many aquarists. If cultured corals from these sources can be obtained then it is recommended to do so. These cultured corals seem to be more hardy than their wild brethren, possibly because they have grown accustomed already to life on a captive reef.

So, where is the formula for how many corals can be placed for X gallons? There isn’t one. It is fortunate that corals do not place anywhere near the bio-load on the aquarium that fish do. The restriction is, as said, that corals are going to grow. Unrelated species touching each other is not good practice. If the reef looks crowded, it probably is, and on a new reef certainly is.

So, the corals are dealt with. It is now up to the aquarist to give time to routine maintenance, and watch the reef grow.

Some aquarists are happy at this point. Others, however, and this is probably the majority, want fish as well. That’s fine, but…

It is recommended that the reef is constructed and ‘planted’ with corals first. This is so changes to the reef (fitting corals and the like) are done as far as possible before any fish make their appearance. The fish will then have an opportunity to settle more quickly without disruption.

When fish are introduced then the bio-filtration will have to work harder. The fish present a higher bio-load than corals in their natural life functions. In addition, they need to be fed which will place a further demand on the filtration (no matter how careful the aquarist not all food will be eaten). So the introduction of fish puts pressure on precious seawater quality. There are restrictions on the number of fish that can be placed in a fish only aquarium. In the reef aquarium, these restrictions are more severe. There is no way the aquarist is going to have an aquarium that has anything like the fish numbers on the wild reef. The aquarium, even if huge by home standards, is less than tiny compared to the reef. Is there a sump attached to the aquarium? Think of the ‘sump’ for the wild reef – countless gallons of ocean. Fish though can be placed in the reef aquarium to great effect, and they make it much more natural in appearance.

So the aquarist is back to research. Individual fish that can be kept depend on the size of the aquarium in the same way as in the fish only system. Bigger fish, particularly surgeon fish etc, need space. Bigger fish also cut down on the number of fish that can be kept. The aquarist, as said, is back to the books and the internet. Make a list of the fish that are appealing in colour and size (fish grow as well!). Be very sure that the fish do not view a coral polyp as lunch. In other words, the fish must be reef safe. Do any of the fish require a specific diet? Can the aquarist deal with that diet? Are the fish compatible (continuous fighting, chasing, and stress are not required)?

Once a list has been prepared, again, a visit to the retailer(s) is in order. Are the fish as expected in colour etc? What are the prices?

The fish need not be purchased in one go. It is better that they are not. During the research, a caution may have been given that a particular fish would be more nervous or shy than normal. If this fish is compatible with the others on the list, then this type of fish is the one to introduce first. It will be settled and at home, and the following fish introductions will be the new neighbours. It is also better to introduce fish gradually allowing the bio-filtration to adjust, so that water quality doesn’t reduce.

So what is the guideline for fish in a reef aquarium? It is my opinion, and the opinion of many others, that ‘less is better’, because of the attention that must be given to water quality. The aquarist should only put as many fish in as he/she can visually get away with, that is, the number that visually the aquarist is satisfied with. In a net 43 gallon reef aquarium, I keep two small fish, (a small damsel and a dwarf angel), though there could be more. I’m happy with that, as I know they are in good health, as are the corals, and the seawater is top quality. For those who want more fish than minimal, then this is the guideline:

Fish load is measured by the inch (excluding the tail) against gallons. The aquarist should know the net gallonage of the display aquarium. If there is a sump, then the gallonage in the sump is ignored. This is because the sump is a water quality enhancement, and the seawater in it should be considered in that way. As said, it is best to introduce the fish gradually. The maximum suggested fish load in a reef should be 1″ to every 6 gallons in the display aquarium. So if the aquarium is small, small fish are best. If the aquarium is large, then, say, surgeon fish and some small fish could be housed.

Don’t give way to the ‘one more fish’ will be ok temptation. It may not be ok, and the water quality will begin to decline, perhaps very slowly. Then there will be a need for more routine maintenance, such as water changes, to keep the reef looking as it should. Don’t put the reef at risk.

If the temptation to buy is strong, then remember that it is a reef aquarium. Once it is settled and has been running a good while, the aquarist can obtain a cleaner shrimp or two, and also some creatures that will assist in maintaining the reef, such as snails and small hermit crabs. These additions will not damage the reef but enhance it if not overdone. Plus, it adds to the diversity of the reef and the overall interest.

Huge aquarium or more modest one, a reef aquarium is of immense interest. There seems to always be something new to wonder at and enjoy.

  1. I enjoyed this article as well.
    Your point about adding fish “The fish present a higher bio-load than corals” is important to many who are considering a mixed reef. The consideration of adding fish should also include baths, dips, or quarantine so as to prevent disease introduction that may be difficult to treat. The new marine aquarist needs to have as much knowledge as possible before starting.

  2. Hi Carl,
    Glad you enjoyed the read.
    We try to be as helpful as possible to new (and perhaps not so new) marine aquarists.
    Treating fish for disease in a reef aquarium can, or should I say usually is, difficult. So placing the fish in quarantine before introducing them to the reef is a good idea.

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