Pentair Pentek RFFE20-BB Big Blue Water Filter, 20-Inch, Whole House Radial Flow Iron Reduction Replacement Cartridge, 20" x 4.5", Pack of 2Brand: Pentek Color: White Features: GREATLY IMPROVES TASTE by filtering up to 3 PPM of dissolved iron. Eliminate metallic taste. PREVENT RUST STAINS on sinks, toilets and plumbing fixtures and prevent appliance damage. WHOLE HOUSE FILTERING on main water line, works great for well water. FITS ALL 20" Big Blue Housing and can replace any 4. 5" x 20" Iron reducing filter REPLACE EVERY 3 MONTHS for 3PPM reduction with a family of four. See image chart