Fluval Carbon is a premium, low-ash and highly porous carbon that is highly effective at removing heavy metals, odors, discolorations, organic contaminants and pollutants from aquarium water. Key Features : Chemical filter media Removes trace metals toxic to sensitive fish, organic contaminants, discolorations and odors Creates sparkling, crystal clear water Made of bituminous carbon - long lasting, highly porous and absorbent Provides large surface area for adsorption of impurities Will not raise phosphate levels Ideal for use with most canister filters Convenient 1,550 g (54.70 oz) format For best results, replace every 4 weeks