Fluval C3 Stage 3 Zeo-Carb is replacement chemical filter media. This is a combination of activated carbon and ammonia remover used to help absorb unwanted odors, discolorations, and other impurities.
This chemical media also helps prevent toxic ammonia from building up in your aquarium. The activated carbon will help reduce the amount of particulate matter and remove any trace amounts of chlorine all while helping improve your aquarium water clarity.
Zeo-Carb packs become inactive over time and should be replaced roughly twice a month to help maintain your water quality.