The biOrb filter cartridge works like a waste bin, trapping dirt and keeping it out of the way of your precious fish. After 1-2 months, the cartridge is full and should be replaced with a new one, and a partial water change of approx 30% should be carried out at the same time. The biOrb service kit includes everything you need to keep the water in your aquarium clear and healthy, comprising of a replacement filter cartridge, an algae cleaning cloth and a sachet of water preparation chemicals.