SeaChem Matrix Carbon is a truly unique activated carbon, bead shaped for optimal hydrodynamics. This provides maximum water flow and contact with a high density of adsorptive sites without the compacting common to granular activated carbon. Matrix Carbon has a very low ash content as indicated by its minimal impact on pH. Even when added to distilled water, it does not raise pH above 7.0. While all carbons contain phosphate, regardless of false claims to the contrary, Matrix Carbon has the lowest leachable phosphate content of all major carbon brands tested. It out-performs other best grade carbons by at least two-fold when compared for total capacity to remove aquarium organic matter, rate of adsorbtion, and duration of use. 250 mL will easily treat 100 gallons for several months. It is very clean and nearly dust free. The 100 mL bag size will fit any filter on the market and treats over 40 gallons. Marine or freshwater use.