The Fluval Ammonia Removers are a natural ion-exchange which is suitable for freshwater only, and have been designed to remove ammonia before it can harm your fish.It is very important that you control the levels of ammonia in your fish tank or aquarium as increased levels of ammonia can cause stress to your fish and in some cases even death.The Ammonia Remover is designed to remove ammonia when levels increase to an unacceptable level. It is recommended that it is used when you first set up your fish tank or aquarium, when you have removed any chloramine, or regularly if you have a higher than average number of fish in your tank.You must also ensure that when using as a regular treatment you remember to replace the Ammonia Remover around once per month as the effectiveness will gradually fade until it becomes inactive.Ideal for all filters, suggested media placement:For use in all 04/05/06/07 fluval external mid or lower level media baskets.FX5/6: top or middle media baskets.