Substrate of some description is more often than not used in the marine aquarium, be it fish only or reef. This gives a more natural appearance at the same time as requiring more effort in maintenance. Some aquarists don’t use anything on the aquarium bottom, simply waiting for natural growth to cover any naked glass. So it’s obvious that a bottom covering is not a requirement in the same way as a heater or protein skimmer.
Sand is the obvious choice for the substrate and the decorative type needs to have a depth of less than 2 inches (circa 5cm). Dirt could build up quite quickly in the sand bed and it needs to be reasonably easy to maintain. As said, if there is no desire for more maintenance, then don’t have a substrate and wait for natural growth to take care of things – some patience is required. If not using sand then rock decorations can be placed more closely to the vertical viewing glasses, ensuring that there is plenty of room for an algae scraper and siphon tube.
So a substrate is required, it’s been decided. First thing is to get the sand and the obvious place is the local store. Bags of suitable sand are sold so there’s not a problem. Make sure the sand is coarse grained, not the very fine stuff. However, the sand is not ready for immediate use. Though it could be stated to be pre-washed, it’s worthwhile cleaning it again to be sure – it’s possible that a bit or bits of metal or other debris could be present. In easily managed amounts give the sand a wash, just tap water will do. Keep the eyes open and ready for anything that doesn’t look like sand! Let the washed sand drain and if it dries out it doesn’t matter. In case any bits of metal have been missed, perhaps a fairly powerful magnet could be passed over it, this will take time as the sand has to be spread out somewhat. Obviously ensure that dirt can’t get in it.
The clean sand can be placed in the aquarium but rocks must not sit on the sand, they must sit on the base of the aquarium. If on the sand the rocks could move and cause trouble. Place the rocks in the aquarium first directly on the aquarium base. Then place the sand, it will be necessary to push it into the crevices that can be seen from the viewing panels, use a small stick, spoon etc if needed. When seawater is put in the sand could wash further causing incorrect and unsightly depth or gaps, so further sand should be placed. It won’t be long before the sand bed is satisfactory. The aquarium will be looking good already!
Once the aquarium is matured then fish will be slowly introduced (unless it is a corals only reef which is not likely). Once settled, the fish or one or two of them could decide to re-model the sand. Fair enough, after all it’s their home. Any changes in the sand appearance caused by fish won’t last because of cleaning, unless they’re well inside the rock formation (another reason for having the rocks on the glass base).
Eventually the sand will begin to show dirt and discolouration, this could be after a few weeks or a good bit longer. The sand is cleaned with a siphon, the straight tube needs to be long enough to reach the bottom without difficulty. Seawater is siphoned with the flow rate controlled so the sand rises in the tube but then falls back, dirt being light continues to rise and is extracted. Obviously a good time for this exercise is at a partial seawater change. If the amount of seawater to be extracted is complete before the whole available sand bed has been done, then do the remaining part at the next partial seawater change. Once a little experience has been obtained siphoning the sand is very straightforward. Also, it’s best to siphon the sand before dirt has penetrated to the bottom, the top layers are easier to deal with than the full depth.
Given time, the aquarium is enhanced by the use of a substrate. The overall effect is natural looking. However, as said, the alternative is to allow Mother Nature to do the decorating though she does want to take her time.