From The Aquarium Wiki
Substrate refers to the material placed in the bottom of an aquarium. Typically it is composed of sand, stone, gravel and various debris. Different aquatic animals require different types of substrate to mimic their natural environment and to make them feel less stress.
- A black or near dark coloured substrate is often best for many fish as it makes them feel more confident in their surroundings, especially if they originate from more murky waters in the wild.
- Sand is used to allow those fish (Puffers) that like to dig into the sand to hide or perhaps to allow them to sift out food particles. For example, some loaches and corydoras catfish do this.
Types of substrate
There are many different types.
- Coral sand - medium fine made up of crushed coral and shells. Intended to help buffer a high pH in marine tanks.
- Live sand - contains live bacteria and fine coral sand for marine tanks.
- B.D. Aquarium Sand - plain sand that doesn't alter pH. Suitable for fresh or marine tanks.
- CaribSea Sand - available in different colours.
There are dozens of different types of gravel available in dozens of colours. Some of the more colourful gravel is actually coated in plastic and may not be suitable for long term submerging in tanks.
- Ecosystems Miracle Mud for marine tanks.
- Floramax - An inert, natural gravel for freshwater aquariums.
- Aquatic soil - Basic pond soil sold by garden centres. A soil which has been sterilised.
- John Innes #3 soil - Basic soil used when constructing a Walstad tank.
Certain fish come from rivers in which leaves cover their substrate in the wild.