Activated carbon is used in aquariums. If activated carbon is used properly, it is one of the effective filters in household and commercial fish farming. However, as in most cases, there are different methods for the activated carbon to choose to place or even use in general according to some situations. Nevertheless, the correct use of activated carbon may be a useful tool for high-quality water quality and healthy aquatic life. Activated carbon has many uses in home aquariums, but popular, it can be said that it is important to remove dissolved organic compounds from water. Dissolved organic compounds (DOC) are the result of decomposition of undecomposed food, food digest and dead fish. Although a small amount of DOC may be, as a source of nitrogen compounds, they may cause water quality problems at higher levels. Dissolved organic compounds contribute to the yellowing of water between changes in moisture and reduce light penetration, which is an important issue when maintaining photosynthetic invertebrates and large algae. Increased DOC levels can also lead to the growth of seaweed, and there seems to be a correlation between stress and certain fish diseases.

Another use of activated carbon is to remove other potentially toxic organic and inorganic chemicals that may enter the aquarium in various ways. The substances that activated carbon at least moderately remove are acetone, alcohol (including isopropyl alcohol), antifreeze, benzene, chloramine, chloroform, chlorine, chlorophyll, citric acid, dyes, herbicides, hydrogen peroxide, insecticides, iodine, Ketone oils, organic acids, pesticides, phenols (including those that produce an unpleasant odor), radon, solvents and tar emulsions. Since at least some of these chemicals are used in fish medicines, especially dyes, carbon is usually removed when adding medicines. On the other hand, using activated carbon to remove traces of treated drugs is a useful application of this material.