Substrate is the word we use for the gravel used at the bottom of a fish tank. It’s beneficial to the tank as it not only mimics the fishes natural habitat, but it’s also required to grow most plant species. You can purchase multiple different brands of all different colours and sizes of gravel. The more serious fish keepers tend to purchase the more natural colours like black, white, and sandy colours. But you can also purchase pretty much any colour. There’s always someone out there who will buy the rainbow gravel.
Shapes & sizes
Gravel can come in lots of different sizes. From pea sized, to fine sand. While sand is harder to manage in terms of cleaning and keeping it settled it can often be a desired substrate. Fish such as catfish which have small barbels, and these can be damaged in larger, more rough gravel. Sand allows fish such as catfish and other bottom dwellers to sift through it safely when they search for food. It’s important to pick the right substrate on a new set up, as it’s difficult to change once applied. Especially if you have plants that have taken root.
Some substrates are often advertised as ‘no dust’ and you can add it straight into the tank. Whereas other types will need thoroughly rinsing as it could cloud your water. More premium substrates often have nutrients included in them. These will be beneficial for starting plant growth without the use of fertilisers, however over time these will diminish.
Soil can be used on the bottom of your tank, with gravel on top to cap it off and stop it leeching into the water. Plant roots will grow down into the soil and benefit for a long time from the nutrients it provides. However soil is very messy, and is only recommended for the experienced. Plants will still do fine without soil. If choosing soil make sure to do your research as some soil wont be safe for the aquarium fish.