Zanyzap's 6 Pack of Ammonia Remover Infused Pads compatible for Fluval FX4, FX5, and FX6 Canister Filters are specially infused with ammonia-absorbing particles that pull harmful ammonia from your aquarium. Each premium filter pad offers both mechanical and chemical filtration, enhancing the health of your aquarium and reducing the risk of disease and stress of your aquatic life. Use these pads to prevent fish loss, outbreaks of dangerous ammonia spikes, and for post medication supplement. Custom made to tightly fit the center white chamber, this filter pad will prevent unwanted bypass and enhance your overall filtration. Zanyzap Ammonia Remover Pads should only be used as a preventative measure. These pads are not a remedy for sustained ammonia concentrations. For best results, thoroughly rinse pad before use and install at last filtration stage, in bottom chamber. Replace monthly or as required after testing water with a water test kit.