The six pack of Fluval Nitrite Remover - 307/407 provides incredibly effective chemical filtration for freshwater and saltwater environments. The foam sponge was designed to support the growth and cultivation of beneficial bacteria which contributes to a healthy aquatic environment and dramatically reduces the instances of fish loss. The foam sponge also traps floating particles such as debris, waste or food. The custom fit of the sponge dramatically increases filtration quality and efficiency. The Fluval Nitrite Remover - 307/407 can be replaced monthly or as required after water testing.