The anti-algae filter cartridge works like a waste bin, trapping dirt, once full it should be thrown away and replaced with a new one. This should be done every 1-2 months depending on the size of the aquarium and the number of fish kept. An anti-algae water treatment in the cartridge polishes the water and removes impurities helping to keep the water clear between changes it has an active life of 8 weeks. Service kits include: 1 new filter cartridge, 1 cleaning pad and 1 water treatment sachet, simply unclip the old cartridge and fit the new one. The Service Kit eliminates the need to cut filter foam, deal with messy carbon and measure out doses of water treatment – simple.