If you are going to buy 20 gallon fish tank, then should know the requirement and should have the maintained water level of the tank. You have to manage the water level in small fish tanks because they need more awareness. As the smaller tanks have small filters and so the water need to be replaced on regular time.

You can avail the products from the market to manage the small fish tanks especially the water level. Of course these products will help you to manage the water level, but it's better to do own management rather, then spending extra money on these stuffs. For better maintenance you have to change the water after every particular time. Never change the water at once, just remove the ½ water of the tank and fill it with fresh water. The same way you can change the complete water of the tank.

You have to change the water with similar natural chemical composition so that the marines and fish will feel the same atmosphere and won't get any trouble. This way you will be able to replace the water with proper compositions and the toxic materials will also be replaced. Clean the filter of the aquarium regularly. This will also help you to maintain the 20 gallon fish tank. Filter cleaning will help you to eliminate nitrate and ammonia from the water. These two chemicals are really harmful for the fishes and marines. With the stated tips you can easily manage your fish tank.