The filter cartridge works like a waste bin, trapping dirt, once full it should be thrown away and replaced with a new one. On average this should be carried out every 6 to 8 weeks but this is dependant on the size of your biOrb and how many or the types of fish it is stocked with. Your biOrb instruction manual will also always inform you of the best time to carry out a filter change A partial water change of 30% should be carried out at the same time to maximize the water quality. Contents: A Replacement Filter Cartridge. Water Preparation Chemicals. Cleaning Pad Aquarium/