The Seachem Algae Scraper Replacement Blades are a direct replacement for the metal blades used in the Seachem Algae Scraper and will fit in the removable scraper cartridge. While these stainless steel blades are durable, they can wear out or lose their smooth edge with frequent use, especially on harder coralline algae deposits. Don't risk scratching your glass aquarium with a worn blade; replace them regularly or with any visible signs of wear. 3-Pack.