Instructions
Cole's Notes: Membrane Replacement.
Only purchase a RO replacement membrane when it's needed unless you think you'll need to replace it shortly and would like to have one on hand. Wet membranes can be stored in a refrigerator for up to 1 year. (Keep it in its sealed, original packaging). If the membrane dries out, it will not produce water.
Under normal use, a membrane can be expected to last approximately 2 years but they should be tested every 6 months or so. A TDS meter can give a good indication when it's time to change the membrane. Measure the TDS of both the feed water and product water. If the rejection rate is 95% or better, the membrane is okay. If not, it's time to replace it.
The higher the rejection rate, the better. A 2% difference in the rejection rate can save you big $$$ in DI cartridges. You'll only need to replace your DI cartridge half as often using a membrane with a rejection rate of 98% versus one with a 96% rejection rate. That's a good reason to buy a membrane with a higher rejection rate like SpectraPure membranes. All of their membranes are subjected to a proprietary process which increases their rejection ratio over the membranes purchased by other vendors, even from the same supplier.
When it is time to replace your membrane, its a good idea to consider boosting the output of your RO unit. For example, the capacity of a 25, 50 or 60 gpd RO or RO/DI can be increased to a 90 gpd just by purchasing a 90 gpd membrane and matching flow restrictor.
Reverse Osmosis Membrane Replacement Guide.

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