There are many reasons for cloudy water. Newly set up aquariums may turn cloudy because of a biological imbalance and will usually clear in a few days if left alone. Do not add any new fish or do any cleaning of the tank or filter. Established aquariums can turn cloudy because of overfeeding, too many fish or inadequate filtration. Adding a larger or second filter, removing some fish and/or cutting back on the amount of food entering the aquarium will often resolve this problem. Also make sure that you are doing regular, at least monthly, water changes. To learn more, watch our video on The Importance of Water Changes.