It's normal to get green algae in a tank. The best way to control it is to vacuum the gravel and change about 25% of the water once a week in such a small tank. Larger tanks can go longer. After you remove some water, you use an algae pad to clean the algae off of the glass. Typically the first 3-4 months of a tank's life is when algae grows the most and it will come under control with regular water changes. In older tanks, it becomes an issue due to overfeeding, lack of water changes, too much or the wrong type of light, and sometimes the tap water being used is an issue. You should not need an air pump, no. Some live plants may help if you are already doing water changes, and only have one or two very small fish that are not goldfish.
Date published: 2019-04-01