Building A Captive Reef – Just Need Rocks?

It can take quite a while getting a reef system together. There are quite a few decisions that need to be made.

The first and obvious one is the aquarium. What size is it going to be, the biggest that will fit or a smaller one that will be cheaper to run but just as interesting? Then, once that is sorted out, will there be a sump or not? When the basic seawater containers are there, the equipment needs to be obtained. Heaters, protein skimmer, maybe a calcium reactor, a lighting system etc. Plus test kits and of course dry sea salt (unless clean natural seawater is available). As time progresses, new aquarists can get impatient. The wallet tends to get thinner too!

The whole of the construction of a marine system is exciting, but not so much as when thoughts of the reef itself arise. All equipment ready, aquarium in position. Let’s go!

There are still decisions to be made and the attacks on the wallet are not over yet. Will the reef be entirely made out of live rock, or will ordinary rock be used? It goes without saying that live rock is the one of choice, but it is expensive and to be effective there must be enough of it and at a high enough quality.

Perhaps a compromise can be reached. Use ordinary rock on the base and live rock to surface the reef. If the ordinary base rock is of the porous variety it will become live. This does take time though.

A point to watch when mixing live and ordinary rock is to be sure there is still enough live rock to be effective. If not supplementary bio-filtration could be needed, at least temporarily.

The rock can be mixed live to ordinary in any ratio, but obviously the more live rock that can be used the better.

Another possibility is to use all live rock, but save on cost by buying live base rock for underneath and premium rock for the surface. Base live rock is pretty boring looking stuff but still harbours the bacteria for bio-filtration. Premium rock carries the bacteria but in addition a potential diverse range of reef life, and it is much better looking.

Another way is to build a support structure from plastic ‘egg-crate.’ This means that there will not be a requirement for any base rock, therefore if live rock is to be used only the premium grade needs to be purchased. It has the advantage of increasing the seawater gallonage as displacement by rocks has been reduced. There is reduced opportunity to build in caves of course as the rock quantity is reduced, and obviously creative design is reduced as the rock formation follows the ‘egg-crate‘ foundation. It can still look very attractive however. Again, care must be taken that there is sufficient live rock for effective bio-filtration.

Anyway, whatever the aquarist has decided, excitement has increased as reef building is here.

If live rock is to be used it is obvious that it needs to be placed in seawater. If it is ordinary rock this doesn’t matter, it can be built dry. In the latter case, when the aquarium is filled with seawater time needs to be given for air bubbles to clear. This doesn’t take long, a few days. The ordinary rock can of course be placed into seawater in the first place.

Now, what is the reef going to look like? No matter how small or large the aquarium there are design choices. There are things to remember though.

Corals, hard or soft, are going to be placed on the reef. They will grow, so the rock structure does not want to be too close to the surface. Fish will no doubt be added and to feel secure they need holes and crevices to hide and sleep in. It is quite easy to incorporate a small cave or two within the rockwork. The different shapes of the rocks help to create holes and crevices.

Very important is the need for good seawater flow within the rock structure, so the reef shouldn’t be built too tightly. It does need to be stable.

Very small aquariums are more restricted in reef shape, they could be restricted to two or three pieces of live rock. These can be put together in more than one way though, and as there isn’t much of it the very best and good looking live rock can be used.

Larger aquariums can allow more imaginative reefs. They don’t have to be a straight run of rocks from one side of the aquarium to the other. That type of design has been likened to a display in a vegetable shop. It must be remembered that it is personal preference that is the rule in design, and if the aquarist wants a run of rocks so be it.

There are other ways though. Perhaps the reef could start high on, say, the left and gradually slope down leaving a good space at the front and on the right for a decorative sand bed. Or perhaps there could be one big pinnacle in the middle (not the exact middle, a little offset one way or the other), with decorative sand all round, and a few live rock pieces placed randomly. If the aquarium is big enough, how about two pinnacles, not geometrically set but one close to say the left and the other offset to the right of the middle. Then comes the sand and the singly placed live rock pieces.

The choice of design is up to the aquarist and his/her imagination. Just remember that corals are going to be placed on the reef so this needs to be considered when building.

Looking at ’featured aquariums’ on different internet sites, the imaginative design of reefs can be seen. With the careful addition of corals the display can be stunning. No matter if the corals are going to be hard or soft types, if they are carefully chosen for colour, shape and consideration is given to potential size, the captive reef that has been built can be individual and very beautiful.

---

Building The Reef

The aquarium is in position and equipment is available. Now comes the most exciting part of all, building the reef and stocking. Reef construction first, of course.

The aquarist may have decided that live rock is just too expensive at the moment and has decided to use an alternative bio-filtration method. In this case the cost is going to be greatly reduced. The rocks purchased will need to be inert (ie. marine safe) and it is unlikely that any marine retailer will sell anything that isn’t.

Before the aquarist jumps in and buys some rock, remember that corals are going to be added and corals normally come attached to rock. This rock will be from the ocean and may bear life forms similar to live rock. It is to most intents and purposes live rock. Perhaps the rock purchased for the reef can be those which are highly porous. If this is the case marine organisms will in time establish homes in and on it. In time it can even become live as bacteria make a home.

On the other hand, the aquarist may have decided to use live rock. The price may have been high, but nevertheless that is the road chosen. There is a way of reducing the cost and that is to buy less and use safe porous rock as well. The proportions can be ½ and ½ or more, that is more live rock. It is worthwhile purchasing premium live rock so it can go on the reef surface, and it is spread reasonably equally over the reef. In time the porous rock should take on marine life and become live. The only potential problem here is the initial bio- filtration. Reef systems, with a view to water quality, have a lower fish load and the bio filtration should initially cope, and with slow stocking the capacity will increase. The aquarist must be aware that the initial bio-filtration is lower and keep an eye out for problems. On initial start up water parameters are regularly routinely tested anyway.

Perhaps the aquarist is going to use all live rock. The usual guideline for the amount of live rock to use is 1 to1½ lbs per gallon of the whole system net gallonage. This is fine, but a problem arises because some live rock is considerably lighter than others. So a different guideline can be used and that is that the reef should be around 2/3rds of the capacity of the display tank. This is often the amount that is to be used anyway to create an attractive reef, and offers the aquarist room to aquascape and also leaves water space for fish. Costs can be reduced with all live rock by buying premium rock to cover the outer reef and base rock for the foundation.

The following is a personal view. Many aquarists place their rocks directly on the aquarium base. I prefer to raise them above the base, say 1″ to 1½”. This allows water to easily access the area. The job is very easy and cheap using plastic ’egg crate‘. (See the text ‘Elevate Your Reef’ under DIY.)

Whether the rocks are put on the aquarium base or not, and whether the rocks used are live rock, a live/inert rock mix, or all inert rock, the following applies. It is important that the rocks are not ’fitted’ together too tightly. Accurate fits are not possible, of course, as the rocks are pretty random in shape. The rocks of the reef should have gaps and tunnels throughout, and their random shapes should assist with this. Having good gaps and tunnels allows water to flow throughout the structure more easily. If there is good water flow then there will not be any area lacking in oxygen or even stagnant. The spaces between rocks afford livestock plenty of hide holes. The rocks also need to be stable to avoid any rock fall.

Putting the reef together can be great fun. When I did mine, I started again at one point, even though most of the rocks were in the tank. Eventually, I achieved what I wanted, and also managed to make a couple of small caves within the structure. I know that the Flame Angel uses one at night.

Particularly with live rock, but also with other rock if desired, it is advantageous to have the aquarium say 2/3rds full of prepared seawater which is heated to the desired temperature. As the rocks go in the water rises. When the rock work is complete if the water is short of the required level it can be topped up. The circulators can be turned on and there’s the reef.

---