You should clean the gravel in your fish tank once a month. With that said, if your tank is particularly healthy and well-balanced, you can get away with only cleaning the gravel once every two months.
You can clean the gravel in your tank by using an aquarium vacuum. Additionally, you should also use a sponge or a scraper to remove excess algae from the surface of the tank. Cleaning the gravel of your tank while performing the regular water changes is ideal.
Be careful not to clean the tank’s gravel and the filter at the same time. Cleaning both at the same time can cause most of the beneficial bacteria in the tank to die, thus, ruining the tank’s nitrogen cycle and potentially harming your fish.
