Aquariums need substrate (sand & gravel) to create a natural-looking environment and to allow plants, corals, and some fish a place to bury into, live, and grow. Here is a guide for picking the best substrate for the four popular aquarium types.

Saltwater Fish Only Aquariums

Substrate in saltwater fish-only aquariums is very similar to substrate in freshwater fish only aquariums. Some fish like wrasses and gobies burry in substrate, but the substrate is mostly for aesthetics. If you are keeping burrowing fish, it is best to have a sand bed made of fine sand deep enough for the fish to cover themselves. A major difference is that with saltwater you should use an aragonite or calcium-based substrate that helps to buffer the pH of the aquarium. We recommend CaribSea Seafloor Special Grade Reef Sand. NOTE: In freshwater, these calcium and aragonite substrates can raise the pH of the water too much and potentially be harmful.

If you do not plan on having burrowing fish, then crushed coral substrate is easier to clean because it is more coarse and harder to accidentally suck out while using a gravel vac. Use CaribSea Florida Crushed Coral.

Saltwater Reef Aquariums

In reef aquariums, many animals can use the substrate. Fish, sea cucumbers, clams, anemones, and certain corals all need substrate to live. All of these animals will prefer a fine substrate like the CaribSea Seafloor Special Grade Reef Sand.

Unfortunately picking a substrate isn’t this simple because many corals such as Acropora and Montipora species do best with extremely high water flow. Fine sand is easily blown around into sand storms and because of this a coarse substrate or even no substrate can be preferable. The disadvantage of this is most people will find it extremely ugly. If you decide that the increased water flow is more important than the aesthetic benefits of substrate then a bare bottom tank without substrate may be preferable.

Freshwater Fish Only Aquariums

Freshwater fish only tanks mainly use substrate for aesthetics, but some fish such as loaches and eels like substrate to burrow into. If you have burrowing fish many of them will prefer a smooth fine substrate that won’t scratch their skin. If you don’t have burrowing fish, a larger grained substrate is easier to clean because fine substrate can easily be sucked out with a gravel vac while cleaning. If you have burrowing fish, provide enough substrate so the fish can completely cover themselves. If you don’t have burrowing fish, only use enough substrate to cover the glass. Any more is a waste.

Freshwater Planted Aquariums

Substrate is very important in planted aquariums. Water plants use substrate like land plants use soil. Plants generally prefer a finer substrate that their roots can easily grow into. Plants also like a nutrient-rich substrate with fertilizer for their roots and a deep substrate so their roots have room to grow. Our favorite planted aquarium substrates are the different varieties of Seachem Flourite.

As a cost-saving measure, some aquarists will use fine sand rather than a soil substrate. If this is the case you can use Flourish Tabs to add fertilizer for the plant’s roots.