Substrate
Substrate
Substrate choice is usually treated as decoration and is often a welfare decision. Corydoras, kuhli loaches and many cichlids need soft sand they can push through; sharp gravel erodes their barbels permanently.
Short answer
The material on the tank floor. It is a habitat requirement for sand-sifting and burrowing animals, a rooting medium for plants, and in the case of active soils an influence on water chemistry.
What it does
- Anchors plants and supplies root nutrition where active
- Provides bacterial surface area
- Habitat for burrowing and sifting animals
- Buffers water chemistry where the substrate is active
Strengths and where it fits
Strengths
- Sand suits sifting and burrowing species and looks natural
- Aquasoil supplies plant nutrition and buffers pH downward
- Inert gravel is cheap and easy to vacuum
Good fit for
- Sand: corydoras, loaches, dwarf cichlids, Tanganyikan shell-dwellers
- Aquasoil: demanding planted tanks
- Inert gravel: general community tanks with epiphytes
Limitations and where it is the wrong choice
Limitations
- Sharp gravel damages barbels and prevents natural feeding behaviour
- Deep fine sand can develop anaerobic pockets if never disturbed
- Aquasoil releases ammonia when new and is exhausted after a year or two
- Coloured and coated gravels can leach
Poor fit for
- Sharp gravel with any barbelled bottom-dweller
Sizing
- About 5 cm depth for planted areas, 3 cm for open areas. AquariumHQ's substrate calculator does the arithmetic.
- Malaysian trumpet snails turn over deep sand and largely prevent anaerobic pockets.