These 12-Pack Intex PureSpa Type S1 Pool Filter Cartridges drop from $69.99 to $24.25 to $23.76 when you enter the code SAVE2 at checkout at VMInnovations. This is the lowest price we've found online with free shipping. These pool cartridges are compatible with Intex PureSpa models: 28403E, 28407E, 28413E, 28421E, 28423E, 28443E, and 28453E. There is no sales tax (except PA, NV, IN, and NE).