Internal Aquarium Filter for crystal clear, healthy water with its intensive physical, biological and chemical filtration. Physical filtration: double-layered Filter Floss Pads reliably remove even the tiniest particles. White side = coarse pre-filter, green side = fine filter. Biological filtration: Filter Foam and Bio Filter Balls with an extra large surface area for the settlement of beneficial bacteria. Chemical filtration: special activated carbon to eliminate water clouding and unpleasant odours. The EasyCrystal Filter is also extremely easy to clean; just replace the filter cartridge every 4 weeks.