Key Features Replacement Crystal Cartridge - a combination of activated carbon and Zeolite. Suitable for SuperFish Aqua Flow 50 Internal Filter Easy to replace and click in place It is recommended to replace media regular to ensure clean and healthy water Assists with crystal clear healthy water with less algae growth SuperFish AquaFlow replacement media has all you need to replace or upgrade your aquarium filter These easy to click in cartridges are a simple straight replacement for the existing Dual Action cartridge in your AquaFlow filters. The cartridges contain a filter a filter foam that also includes activated carbon that absorbs toxic substances from water (Will not fit the AquaFlow XL)