Keep your spa water clean and Intex purespa performing at its best by using genuine Intex purespa type s1 pool filter cartridges. This is the authentic replacement cartridge for your Intex purespa. It works with all Intex pure spa models including 28403e, 28407e, 28443e, 28453e, 28421e, 28423e, 28413e, and 28453e. Replace your filter cartridges regularly for the best results. It is recommended that you replace cartridges every 2 weeks to maximize your spa's performance. help ensure the longevity of your Intex purespa by regularly choosing Intex purespa type s1 pool filter cartridges.