Recommended aquarium sizes are approximate. In many cases, single, double and triple capacity modules can be used with great success in higher volume applications. Single capacity filter features the Lifegard exclusive combination mechanical and chemical cartridge. Internal carbon chamber has retainer screen to prevent carbon from escaping into system. Carbon can be easily rinsed while inside chamber. Double and triple capacity units feature mechanical cartridge only. Water is forced through the filter pleats under pressure, trapping particles from 20 microns down to 5 microns on the outside of the cartridge. Economical replaceable pleats eliminate costly cartridge replacement. Highest quality PVC molded parts.