STAGE 3 – TWIST-IN RO MEMBRANE FILTER CARTRIDGE. Aquatic Life Twist-In TFC RO Membrane Filter Cartridge, 100 GPD: Recommended replacing every 1-2 Years. The RO Membrane reduces impurities known as Total Dissolved Solids (TDS) from the water down to 1/10,000 of a micron, reducing arsenic, lead, parasitic cysts, copper and more. Working Pressure: Minimum 35 PSI, Maximum 80 PSI, Ideal 65 PSI. Flow Rate: 100 GPD.