Pre-Filter Set 10" - Stage 1-3&6 Bundled APEC Ultimate high capacity pre-filter set is made in USA with high quality filtration components to provide a longer lasting filter set to protect and prolong the lifespan of your reverse osmosis system. Premium quality filter set lasts over 12 months for fewer filter change outs and high performance impurity removal. These standard size filters are compatible with APEC RO-PH90 and all other 10" standard size under counter RO systems All US Made Super High Capacity Filters 1st Stage: High-Grade 5 micron 10" high-capacity polypropylene sediment filter -removes dirt, particles, and rust. 100% pure polypropylene depth filter with exceptional dirt-holding capacity translates to longer life and fewer change-outs than existing string-wound or resin-bonded filters. 2nd and 3rd Stage: Premium Extruded Carbon Block 10" - gets rid of unpleasant chlorine, tastes, odors, cloudiness and colors. Also removes VOCs and other common impurities from the water. APEC's extruded carbon block filters consist of activated carbon particles fused into a uniform block with enhanced absorptive capacity and efficiency. Unlike granular activated carbon (GAC) filters, these extruded carbon block cartridges will not channel or bypass due to the extreme uniformity of their extruded activated carbon core. 6th Stage: 100% USA-Made high purity 10" inline calcium carbonate to effectively neutralize acidity. pH Filter The FI-PHPLUS-QC is a 10" inline filter that adds high purity premium grade calcium minerals to enhance the water taste for people who prefer drinking mineral water. This mineral cartridge adds only 100% USA-made high-purity calcium carbonate to effectively neutralize acidity and raise pH in the water. Other re-mineralization filter will claim to add various beneficial minerals back into the water; however, their mineral formulations are often from unknown sources.