Seachem MatrixCarbon 250 ml. - 8.5 fl. oz. Is a truly unique activated carbon. It is formed as a spherical bead for optimum hydrodynamics, and will not pack. It permits maximum water flow and contact with it's high density of macroporous binding sites. Matrix Carbon has very low ash content as indicated by it's minimal impact on pH. Even added to distilled water it does not raise pH above 7.0! While all carbons contain phosphate, regardless to claims of the contrary, Matrix Carbon has the lowest detectable leachable phosphate content of all major carbon brands tested. Matrix Carbon outperforms other high-grade carbons by at least two-fold when compared for total capacity to remove aquarium organic matter, rate of absorption, and duration of use. 250ml treats 400L (100 gallons). Mari