Types of Substrate for an Aquarium

Substrate, the general term for the gravel, sand or other material in the aquarium bed, serves three main purposes. Fish may camouflage themselves against the substrate's mottled colors, or bury themselves in it to hide from bigger fish. Substrate provides a base for growing live aquatic plants or for anchoring artificial plants in freshwater tanks. It also maintains proper biological filtration by giving beneficial bacteria a place to neutralize harmful chemicals in the water. Each kind of substrate is suited to a specific aquatic environment.

  1. Aquarium Gravel

    • Gravel is the most popular type of aquarium-base covering for freshwater tanks (it should not be used in saltwater tanks). Gravel is available from aquarium dealers and pet stores in a variety of colors, from natural to fluorescent pink to black. All gravel should be washed thoroughly in a bucket until the water runs clear to remove dyes or sandy particles that could adversely affect the aquarium. The pebbles should measure about 1/8 inch; smaller pebbles will get caught in under-gravel filters while larger pebbles allow food to fall into crevices and pollute the water.

    Calcareous Sand or Gravel

    • Calcareous substrate contains high levels of calcium that can upset pH levels in freshwater aquariums. It should only be used in saltwater tanks, where the calcium will help to maintain proper water conditions. Aquarists setting up cold-water saltwater tanks can collect sand and gravel directly from a local beach. Naturally collected material should sit in a bucket for a few days (after which time the microorganisms in the gravel will have died), and be washed in fresh water thoroughly before use.

    Coral Sand

    • Coral sand is simply pieces of dead coral crushed to resemble coarse white sand and should only be used in saltwater tanks. It provides an authentic substrate for coral-reef aquascapes and fish tanks that replicate a natural environment. It is often more expensive than calcareous gravel.

    Crushed Seashells

    • Pieces of broken seashells, either bought from an aquarium shop or collected in the wild and sterilized, offer an alternative to expensive coral sand. Aquarists can also mix their own substrate by combining crushed shells with coral sand or calcareous gravel. Seashells, like coral sand, are calcareous and should only be used in saltwater tanks.

    Oolite

    • Sometimes called oolitic limestone, this calcareous rock is characterized by the rounded shape of its particles, each slightly larger than a grain of sand. Oolite is either harvested from inland quarries or from coastal deposits. When crushed into coarse substrate oolite is suited to saltwater aquariums.