Marinium Black Crystal is a high-quality activated carbon that is used to remove organic pollutants, toxic gases, heavy metals, and odors in marine and freshwater aquariums. The yellowish color that is common in the water is also easily removed with the use of activated carbon, allowing for better light penetration throughout the water column. Marinium Black Crystal is produced from steamed coconut shell with a high iodine number rating of more than 1000 mg 12/g. Due to various pore sizes, large and small organic molecules are being absorbed, making it suitable for aquariums with delicate corals and plants. Being pre-washed and sealed in a filter bag, Marinium Black Crystal is ready for instant use.