Freshwater and saltwater fish demand a clean, almost pristine environment. Essential to keeping your aquarium healthy is proper filtration. Even over a short period of time, filters and filter cartridges become dirty and virtually clog, diminishing water flow and filter effectiveness. You should therefore change your filter cartridge on a regular basis to avoid problems that can become very serious, very quickly. Aquarium Pumps and More has replacement filter cartridges for just about every power filter we sell. We strongly recommend that you order replacement filter cartridges when you purchase your power filter or protein skimmer. It will save you a lot of headaches down the road, and your fish will thank you for it!