Hydro Logic Stealth-RO100 Membrane (HL22120)Note: This replacement membrane is only compatible with Hydro Logic RO100 & RO200 filters. Use the Stealth RO Replacement membrane when your flow rate decreases or your PPM increases. The Stealth RO membrane will remove 98%+ of PPM of Total Dissolved Solids. Replacement Directions: Discard all water to drain for 1 hour prior to use. The Stealth RO100 uses one membrane and the Stealth RO200 uses two membranes.