Pentair Pentek RFFE20-BB Big Blue Water Filter, 20-Inch, Whole House Radial Flow Iron Reduction Replacement Cartridge, 20" x 4.5", White, greatly improves taste by filtering up to 3 PPM of dissolved iron and eliminates metallic taste. It prevents rust stains on sinks, toilets, and plumbing fixtures and prevents appliance damage. It provides whole house filtering on main water line and works great for well water. It fits all 20" Big Blue Housing and can replace any 4.5" x 20" Iron reducing filter. It can be replaced every 3 months for 3PPM reduction with a family of four.