The Carbon Filter Media for the BioCompact 50 or FiltoSmart 200 or 300 includes two replacement carbon filter media allotments. Carbon Filter Media transforms unpleasant substances without endangering the aquarium inhabitants. It regulates the pH value and water hardness. This filter media reduces phosphates to inhibit algae growth and clarify water. Activated carbon impressively absorbs unwanted substances in aquarium water, such as medication residues. Activated carbon even helps to remove yellow tinge from the water with no problems. Each allotment contains 4.6 oz of activated carbon. Timing to replace the carbon filter media varies upon aquarium size, number of fish and plants, and declines in filter performance.