Estimating the volume
If you are interested in estimating the exact volume of used rocks, you can do that with the following procedure: place a large empty container on the floor. In this container place a bucket filled to the brim with water. Now put the rocks into the water one after the other, so that a certain quantity of water flows out of the bucket. After every rock you put in, the water has to be replenished by filling the bucked again. The water in excess will accumulate in the bigger container and therefore it is easy to determine its volume at the end (in case of determining the volume of living rocks, it is of course better to use sea water). Once the operation is finished, you should make a note of the exact volume occupied by the rocks, to be able to remember it at the opportune time. It can, in fact, be very useful in the future to know exactly how much water is contained in the aquarium. Under the rocks it is advisable placing a sheet of a material that is resistant to sea water, to protect the bottom glass. This can be made of polystyrene, PVC, or acrylic. Be careful not to leave any grains of sand or other materials under it, because the consequences could be fatal.
Attached or simply piled up?
The next question that we ask ourselves is: “to attach them or to simply pile them up?” In this case, there are discordant opinions, because both of the solutions have advantages and disadvantages. The simple piling up of the rocks is definitely quicker, although the aesthetic result rarely gives much gratification. Often the rocks are just leaning on the rear glass. Once it is all covered in corals it certainly does not look boring, but positioning the rocks in a more planned way can result in more scenic underwater landscapes. The advantage of a simpler arrangement is that later, every single rock will be easily removed. Such an opportunity might be appreciated in case annoying Aiptasias, small anemones, or hydroid polyps should appear. Once fixed, it becomes difficult to remove individual pieces, even though in this way it is possible to create truly sensational structures. We could, for example, reproduce a small snippet of the coral reef in 1:1 scale, or we could create a miniature reef, with all the various components, from a more exposed reef to a wall, or a peak, or if you want even a lagoon. In the middle, you could maybe create a narrow canyon that disappears towards the back. Just get inspired by looking at pictures of a natural reef. Making a drawing can be very useful for accurately collocating the rocks. In freshwater aquariology it is normal to use this system to make a project of the exact placement of the plants. So why not do the same in reef aquariology? In this phase, we should already consider which corals and invertebrates we will want to add to our aquarium. Soft corals need more space than hard ones, because they grow faster. Hard corals need more light than the majority of soft corals. We should already think of all these factors from now. It is useful to remember that soft corals have their own rocky under-layer, for which there should be space in the aquarium. Even the volume of the colonies of invertebrates is often forgotten while planning. Many aquariofiles make the same mistake in this phase: they use too many base rocks, and later they will find themselves forced to gradually take some out. This also depends on the fact that at this stage there still isn’t any water in the aquarium. Sea water, in fact, has the has the optical property of reducing distances making everything appear larger than what it really is. This effect is immediately perceived as soon as we have filled the tank; in this way the whole arrangement will appear closer to the front glass of about a third. The entire thing will then look more voluminous and this effect should be kept in mind when planning. If while you are putting together the arrangement you feel that you have bought only half of the necessary base rocks, then the total volume is probably just right. After filling the tank with sea water, add the living rocks and the arrangement will be complete.