Substrate is a necessity for any aquarium ecosystem. Generally, it is recommended to have 1-2 inches of substrate in any aquarium, however this is all dependent upon the population of the tank. Substrate provides a minuscule but efficient natural filter. As any leftover food and stool falls to the bottom of the tank, it is anchored to the substrate and slowly decays. If the substrate is not frequently cleaned, the decaying matter can create a film, or a white clear substance, that will sit on the top of the substrate. The decaying matter produces a strong amount of good bacteria (as well as bad bacteria) that grows on top of the gravel.
When freshwater aquarium gravel and rocks are used, it is recommended to use kits, pH adjustment products, and appropriate filter media to achieve and maintain desired water conditions. Smooth pebbles in a variety of colors are available to highlight various fish and plants. It is suggested to avoid very light colored substrates, as they can make fish appear less colorful. You can use substrate to create a depth and perspective in your tank. Slope the substrate from back to front, and utilize some terracing to provide deeper areas. This sloping and terracing also profits plants, which have bulkier root systems.
For planted aquarium substrate, a size range of 2 to 5 mm is ideal for most plants. The average recommended depth for most plants is 2-3 inches. You can use larger pieces of rock or gravel on top to help anchor the plants down. The amount of plants is usually limited due to their sizes and how they are anchored. Plants serve as a major contribution to the equilibrium of the tank if taken care of properly. They absorb carbon dioxide and nitrates (the end product of the nitrogen cycle), give off oxygen, and provide nourishment for many aquarium fish. The type of substrate needed is more defined by the species and origins of the plant.
While most fish thrive with a variety of pH, there are fish with specific pH requirements. Substrate is a key player in adjusting pH levels in the water. Typically, freshwater African Cichlids prefer a higher pH, closer to 8.0 – 8.2. South American Cichlids, Discus, Tetras, Angelfish, Rays and some aquatic turtles typically prefer a neutral pH, such as 7.5. There are exceptions to these rules, however. Neon Tetras, in particular, are usually a crowd favorite, and they like a lower pH, closer to 7.0. Adding driftwood and plants to a tank will lower the pH level. Adding lava rock and shells to a tank will increase the pH levels.
Certain fish live in between saltwater and freshwater areas. This is right where the river meets the ocean. These fish prefer a low salinity level, usually referred to as brackish. Their substrate ranges from rocks to sand. The salinity in a brackish tank is easier to maintain if there is sand in the tank. Live sand (such as what is used in a marine tank) is not necessary, although it can benefit the water and ecosystem in your tank. Be sure to have at least one inch of sand in the tank or 2 inches of gravel.
Salt water (marine) tanks have two common choices for substrate: aquarium sand or crushed coral. It is beneficial to use live sand, as it is already cultured with bacteria and will speed up the cycling process. Typically, a thicker sand bed of 2-3 inches is recommended. When using crushed coral as a substrate, depth is not as crucial. A depth which is visually pleasing is typically used.
Making the right substrate decision will not only aid in the health of the aquarium but also make it much more enjoyable to watch.