These algae Scraper blades are compatible with all Sachem algae scrapers. Install the blade by snapping open the scraper cartridge (using the divot found on both sides of the cartridge), placing the blade and easily snapping it back together. The cartridge easily slides out of the Scraper, is able to be positioned in two different heights as well as a third position that hides the blade safely away when not in use. These metal blades will remove tough algae with ease and come with three in a pack. Although these scrapers are a necessity for any aquarium The blades should not be used on acrylic tanks as they may scratch them.