Choosing the Right Substrate for Your Fish Tank

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Choosing the Right Substrate for Your Fish Tank

It’s important to choose the right fish tank substrate since it can have an impact on everything from the water’s chemistry and filtration to the health of the aquarium’s inhabitants.

Water Chemistry

If you need to alter your tank’s water chemistry, selecting the right kind of substrate can help you do the job naturally instead of using chemicals. The right substrate can create beneficial bacteria, release substances, absorb substances or create certain conditions by reacting with other substances present in the water.
For example, you can buffer your aquarium’s pH by adding crushed coral or coral sand, since they both have calcium carbonate to raise the level of hardness of the carbonate. Crushed limestone, marble and shell grit can also be used to increase the water’s hardness.
If your fish need soft water, consider adding peat. It’s a natural way to help the water obtain the same water chemistry as that found in soft water habitats.

Fish Behaviour

Something as simple as the colour of your substrate can have an impact on the behaviour of your fish. For example, dark substrates can really set off the colour of your fish and encourage them to behave less timidly.
If you plan on breeding your fish, remember that some fish will eat their own eggs or the eggs of other fish. Dropping a layer of marbles can help since the eggs fall between the gaps, safe from the fish in the tank.
Also remember when selecting substrate that some bottom-dwelling fish use substrate to hide. It’s important to choose fine grain substrate to avoid injuring the fish.


If you plan on including plants in your tank, be sure to select a substrate that will remain loose. If it becomes packed, the plant roots may not be able to break through. Avoid sharp substrate or anything chemically treated. Instead, choose a fish tank substrate like fine gravel and spread it so that it’s at least 5 centimetres deep.
It’s not uncommon to choose two layers of substrate if you want living plants in your fish tank. Under the gravel, try something richer to help nourish your plants. Choose potting soil, peat, vermiculite or clay.

Freshwater vs. Saltwater

Gravel is by far the most popular choice for freshwater tanks. You can find it in many colours and sizes, making it easy to match your décor or bring out the colour in your fish. It’s important to use aquarium gravel since it’s chemically inert.
Saltwater tanks benefit from substrate that originates from the ocean and is high in calcium content. Consider coral or reef, shell-based substrate, or aragonite. You can find them in a wide range of colours and in fine or small grain with medium to course textures.
Choosing the right substrate for your fish tank is about more than just good looks. You have to consider the type of fish that will be living in the aquarium, whether it’s freshwater or saltwater, the impact your preferred substrate will have on the water’s chemistry and fish behaviour. A fish tank’s substrate can do double-duty as aesthetically-pleasing as possible and is a good way to keep your fish healthy.