Scrubbers Gravel Vacuum Thermometer Carbon Also known as charcoal, carbon is used in most filtration systems and devices. In other systems, a filter cartridge will hold the carbon. Aquarium odors, chemicals, and dissolved waste are trapped inside the pores of the carbon. It is used to remove medication residue, discoloration, or cloudy water.
Carbon needs to be changed regularly.
Activated carbon will no longer effectively absorb anything after about 3 to 4 weeks and should be replaced. Check its effectiveness by putting aquarium water in a clean, clear glass. Place the glass on white paper. If the paper looks yellow through the glass, it's time to change the carbon. If you need to medicate your aquarium , you'll need to remove the carbon or filter cartridge when treating your sick fish.