Blue Planet Filter Box for 20L Aquarium Blue Planet Filter Box for 20L Aquarium Pack is a replacement filter cartridge suitable for use in the Blue Planet Classic 20L fish tank. This handy filter box contains media including wool, charcoal, and bio-balls to help remove harmful bacterial and maintain fresh and clear water and a habitable environment for your fish. The key features of the Blue Planet Filter Box for 20L Aquarium are: Replacement filter box including lid and cartridge media. Media contains wool, activated charcoal, and bio-balls. Activated charcoal removes nasty odour build-up and cloudiness from tank water. Bio-balls for biological filtration and to help break down ammonia. Suitable for use in Classic 20L aquarium. Reduces harmful build-up from food residue and pet waste. Supports aquatic life with a bacteria-free environment. Helps maintain a longer and higher quality of life for fish. Dimensions: 22cm x 7cm x 5cm. Blue Planet products are distributed by Masterpet, a company with over 50 years of experience. Created on the belief that life is just better with a pet, they strive to develop specific products for the specific needs of pet owners. Their products are always known for their quality and reliability.