Fluval Lab Series Opti-Carb's mixture of ion-exchange and synthetic organic removal resins combine with research grade carbon to create a powerful, adsorbent water polishing media. The mixture was formulated for reef aquariums, excellent for fresh and marine environments. Opti-Carb offers superior, rapid reduction of dissolved organic matter, the removal of proteins before they break down into toxic compounds, and elimination of odors and discolorations that result in sparkling clear aquarium water. Opti-Carb can be used as a daily filter media or for removal of specific toxic metals and compounds. It treats up to 50 US gallons, and does not affect pH, KH or General Hardness.