Aqua One PremiumCarb is an Activated Carbon that is Phosphate free and can be used in all types of filtration systems! Pressured Canister Filters, Hang on Filters, Internal Filters and Wet/dry Filters just to name a few. It is suitable for both freshwater and saltwater aquariums. PremiumCarb is a maze of microscopic pores produced by the activation process. These pores absorb minute particles held in suspension in your aquarium water. As the water passes through it the carbon 'traps' the minute waste particles in its pores, and consequently removes them from the water. Aqua One PremiumCarb is manufactured using the highest quality raw materials, as a result it is capable of quickly and efficiently removing dissolved organics and waste from your aquarium water. During its production the carbon is steamed, which enlarges the pore size and surface area. This process is referred to as activation. The microscopic pores in Aqua One PremiumCarb eventually fill with waste. Once they do, they begin overflowing, and releasing some of the waste previously absorbed back into your aquarium. It is therefore essential you remove the carbon once it has been used.