Replace RO membrane with 2 TDS but only 86% rejection rate?

skp

New member
Hi Guys,

My DI is used up, so I'm replacing it but I'm not sure if I should replace the ro membrane. The ro membrane has been used for 5 years making about 3.5 gallons per day. My tap water is at 15 tds and the water coming out right after the membrane is at 2. That means it has a rejection rate of less than 86% and I've been reading that it should be changed when the rejection rate drops below 90%. I didn't test the rejection rate when it was new but I've used a 2 canister ro system without the di before and it was always around 2-3 where I live and I remember hearing/reading that it's normal to get a tds of 2-3 with just ro.
 

Opus123

Member
Hi Guys,

My DI is used up, so I'm replacing it but I'm not sure if I should replace the ro membrane. The ro membrane has been used for 5 years making about 3.5 gallons per day. My tap water is at 15 tds and the water coming out right after the membrane is at 2. That means it has a rejection rate of less than 86% and I've been reading that it should be changed when the rejection rate drops below 90%. I didn't test the rejection rate when it was new but I've used a 2 canister ro system without the di before and it was always around 2-3 where I live and I remember hearing/reading that it's normal to get a tds of 2-3 with just ro.

I've never heard of getting 2-3 reading from just ro, but I've never researched it.

I really don't know what to tell you. You will have to make the financial decision yourself. With your current tds you will get between 1500 and 2200 of 0 tds water from a di cartridge. If you do buy a new ro membrane and you are still getting a tds out of it of 2, then you have wasted money. I get 5+ years out of my ro membranes but I'm working with tap water of 400-450 tds. With your 15, you should get much longer and 5 years. This of course assumes you are changing out the carbon filter when needed.
 

skp

New member
I changed my RO membrane and now I get 0 TDS after the RO and before the DI. There was some gunk in the RO chamber and so I did a bleach soak and rinse. Is that normal or does it mean that I wasn't replacing my sediment and carbon regularly enough?
 

Vinny Kreyling

Premium Member
IF you do not flush the carbon filter before running through the membrane that could be it.
You need to disconnect the line after the carbon filter before it goes into the membrane & let the water run until there are no more fine particles being flushed out. Like rinsing regular carbon before use.
 
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