When to replace RO Membranes?
- Thread starter mike550
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Acceptable rejection rate is 98% of incoming TDS, so if your incoming side says 498, and you're reading 1-2 on output, the membrane is likely fine. If you're reading 318 and the output of the RO membrane is 7-10, it's probably time to replace it.
The RO membrane is really the workhorse of the system. It removes most of the TDS, some membranes to a greater extent than others. For instance, 100 gpd Filmtec membranes have a rejection rate of 98% (i.e., they reject 98% of the dissolved solids in the feed water). So the purified water coming from your 100 gpd membrane would be about 2 ppm (a 98% reduction) if you fed it 100 ppm water. The lifespan of an RO membrane is dependent upon how much water you run through it, and how “dirty” the water is. Membranes can function well for a year, two years, or more. To test the membrane, measure the TDS in the water coming into the membrane, and in the purified water (permeate) produced by the membrane. Compare that to the membrane’s advertised rejection rate, and to the same reading you recorded when the membrane was new. Membranes also commonly produce purified water more slowly as their function declines.
Last edited:
Syntax1235
Valuable Member
Product water changes for me with the seasons due to the temperature of the incoming water. I see much faster production in the summer as opposed to winter, all due to summer’s warmer water here in Maine.
I have always used rejection rate to guide my membrane changes. I was not aware that production could be used. Do you live in a place with constant water temp? Or do you have your ro membrane plumbed into both your cold and hot water lines?
KStatefan
5000 Club Member
@Buckeye Hydro has a calculator on his website for the temperature correction. It can vary a lot. My water ranges from about 45° F to 75° F summer vs winter.
xabo
Valuable Member
I live in Washington D.C. We have the 4 seasons of weather. My unit is plumbed to the cold water line only.
CALCULATOR:
Input your info and compare what you should be getting to what you actually produce.
Input your info and compare what you should be getting to what you actually produce.
Reef Stallion
Active Member
I always learned that RO output should read 7 or less. Once it starts to climb, replace it. Good rule of thumb is to check it when it's new. Once the number starts climb, replace it. I would imagine how much water you run through it affects it as well as how often you flush the membrane chamber. Many units come with the ability to flush it as a way of extending the life of the membrane.
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