When changing your aquarium gravel it is important to preserve the biological balance of your aquarium. We advise that you reduce the amount of food you feed your fish for a couple of days before and after you change the gravel; Re-use as much of the existing water in the tank as possible; Use a biological filter aid to help re-establish the biological balance in your aquarium. Remember to treat any new tap water you use to top up your aquarium with a tap water conditioner. Suitable for all aquarium setups including Coldwater, tropical and marine.