Stealth-RO150/300 RO Membrane reduces 89%+ of PPM of total dissolved solids.
There are two indications as to when to change your membranes.
1. Test the RO and source/inlet water to see what percentage of the inlet waters PPM the 150 is filtering out (rejection %). You should see approximately 98% of the inlet PPMs being removed when the membrane is new. If the rejection % falls under an acceptable level (typically 90%) its time to change the membrane.
2. When the flow rate of the product water slows down significantly. This can also happen if your pre-filters are clogged. If you change your pre-filters and the product water still flows slowly then its an indication you need a new membrane.
When in doubt contact Hydro-Logic.