The scalper cartridge houses a 3 in 1 design. It easily attaches to your both sizes of Seachems algae Scraper and retracts when not in use. The scraper is safe for salt and fresh water. The pad is the first choice when cleaning an acrylic tank, although the plastic can be used, Caution should be taken when working around gravel. The blade attachment easily glides over aquarium sides removing anything that may be clinging to it, but should not be used on acrylic tanks!