Aquarium Components: Substrate
Many different materials including gravel, sand, soil (for some planted systems) or crushed coral can be used as substrate, or bottom material, for an aquarium. The species of fish, and even the presence of plants, may influence the choice of substrate. Crushed coral, for example, may be suitable for an African cichlid tank since these fish require a relatively high pH, alkalinity and hardness. However, angelfish, which come from relatively low pH, soft waters may not tolerate the coral's influence on the water quality. Particle size is of consideration, especially for fish that build nests for breeding or bury themselves in the substrate. If using an under gravel filter, sand which is smaller than the filter slots will fall through, eliminating the space below. Plants must have a substrate in which they can adequately root.
Only substrates that are aquarium-safe should be used in order to avoid leaching toxic substances into the water. Substrate such as gravel or sand that is collected in nature can transfer undesirable bacteria or decaying organics into the tank. Before use, rinse any substrate thoroughly until the water runs clear. Do not use soaps or chemicals to clean substrates. Approximately two inches of substrate is sufficient for most fish but species-specific behavior may dictate a shallower or deeper bed of material.
The color of substrate is left to an aquarist's tastes. However, if trying to highlight the fish, dark-colored substrates generally enhance the appearance of the fish. Light-colored substrates tend to make the fish appear paler while brightly colored substrates tend to detract attention from the fish.