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. Matrixcarbon 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, matrixcarbon 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 adsorption, and duration of use. Marine or freshwater use.