ORNAMENTAL ROCKS IN REEF AQUARIUMS – Part 2

Synthetic ornamental rocks

Be careful also with “synthetic” aquarium rocks, especially when it’s not clear what material they are made of. Some rocks of this kind give more the impression of hardened industrial waste than of a real ornament, and even if sometimes it is possible to integrate them in a reef aquarium, they are not an ideal substitute. We should always remember that our aim is to make the delicate coral polyps grow in our aquarium. For these organisms, in fact, even the smallest concentration of certain substances, which are innocuous to fish and other inhabitants of the aquarium, are often lethal. Skeletons of dead corals were very sought after in the past. Fortunately this trend has changed in time and only rarely we still see coral skeletons in aquariums. Even though the laws for the protection of the species forbid them, this is not the only reason to strongly advise against their use. Arrangements with dead corals are part of the aquariology of the 60s. This skeleton based decoration was used at the time to replace not rocks, but live corals. Today, a similar “cemetery” of corals would not be up-to-date, and it would rightly raise criticism against this hobby. However coral skeletons should not be used in reef aquariums also for another reason: algae eater animals need smooth surfaces to feed. This is true for fish as well as sea urchins or other herbivores. A similar coral skeleton could be very problematic if filamentous algae should appear. On these extremely branched skeletons, the annoying algae are very difficult to remove. Synthetic foam, which to this day is used as a substitute for coral material, is not recommended. With this material one can definitely create structures which are very similar to the natural ones, but not only we cannot completely rule out the presence of substances that are bad for the water, we would also have to do without the crucial internal life that instead we find in abundance in living rocks. It is necessary to observe that these artificial rocks have in the best of cases the charm of fake flowers, and that therefore have nothing to do with a coral environment. However, taste is a personal factor! To help with the expenses necessary for the arrangement, dry and living rocks can be combined. Dry rocks can be used to create a sort of base, attaching them to each other. Non-living rocks can constitute up to 60% of the necessary material, and the arrangement will be completed with living coral material. In this way, enough living rocks are introduced in the environment, and at the same time it is possible to limit the costs.

The calcareous rock that is too thick offers few possibilities to the colonizing bacteria.

The calcareous rock that is too thick offers few possibilities to the colonizing bacteria.

Farmed living rocks

Another solution is farmed living rocks, which however are not yet available in every country. Following the already existing limitations on the import of living rocks from the countries of origin, and their very possible future tightening, these farmed rocks will be soon regularly available here as well. At this moment this material is mainly produced in the southern U.S., especially in Florida. The technique consists only in depositing in the coral reef some calcareous and porous rocks, and waiting about two years for the coral organisms to colonize them. At the end it is very difficult to distinguish them from those that really have formed in the reef. Choosing the rocks, it is recommended to check their porous structure. This is true for both natural living rocks and for farmed ones, and clearly also for dry rocks. The more porous they are, the more extended the internal surface will be, and the more their biological activity will be in the future. Of course it needs to be said that rocks are usually sold by weight, while for the aquarium the occupied volume is more important. But with lighter rocks it is possible to save a lot of money. How much living rock should be used for an aquarium arrangement? It is impossible to answer this question in kilograms, as we are interested in their biological vitality. If we assume that we are talking about good quality living rock, then a third of the total volume of the aquarium should be enough. In any case, the ideal solution is the exclusive use of living coral material. As in many cases this choice is ruled out by financial reasons, we try to solve the problem by making the base arrangement with dry rocks (for example two thirds of the total), and finishing it later, after the aquarium has been filled with sea water, by introducing living rocks (one third of the total volume).

Part 3 will follow