Seachem Purigen is an extra fine filtration media which you can place into a fine mesh bag and then put inside your filter. As water passes through the filter it then gets to work absorbing the nitrogenous organic waste that is present in your tank. By removing this waste it then controls ammonia, nitrate and nitrite, preventing them causing major problems in your tank.
Purigen will gradually turn a dark brown (which indicates it is full of waste) as it works in your tank but this does not mean it is finished! All you need to do is soak it in bleach. Then you treat it in a mixture of water and Seachem Prime for complete rejuvenation.
Purigen is designed for both marine and freshwater use.