Should I replace my RO membranes? the blue ones on top.

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Leon Gorani

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I have a 5 stage Rodi system with a 150 gpd ro membrane addition on the top of the 75 that came with the system. I only make about 60 gallons a month, so around 700 gallons a year. I have had this system running like this for 2 years now. should I change the top two blue ro membranes? I have never changed those, I've only changed all of the other filters underneath.

I am setting up a new tank and want to have the best water possible. My current tds meter is showing 0 tds when I make Rodi water. so I am not sure if I need to change it or not. should I replace them just to be safe since its been 2 years? here's a pic of my set up, I am talking about the two horizontal filters on top. thanks

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Leon Gorani

Leon Gorani

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Need to test tds after ro(before di). If it is very low there then dont change.
so if I switch the tds meter to "in" would that test it before the di? my di resin is in the last far right pod, and the blue line going into that comes out from the top ro membrane, then going into that last chamber on the right. and where that T connection is is where the meter reader is placed.
 

mdb_talon

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so if I switch the tds meter to "in" would that test it before the di? my di resin is in the last far right pod, and the blue line going into that comes out from the top ro membrane, then going into that last chamber on the right. and where that T connection is is where the meter reader is placed.
Ah yes if that is setup correctly then the "in" should be after the ro but before DI.

Normally you will have some TDS there and how much is going to depend on the membrane. In any case 0 tds after the DI is what you want. The only possible reason to change is if it is high TDS out of ro membrane then it uses up your DI resin fast.
 

Mike konesky

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I'd put the 'in' sensor before the membrane, and the 'out' after the membrane. That will give you the rejection. If it's less than 96%, change the membranes. Put the sensors back where they were before testing membranes.
 
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mdb_talon

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I'd put the 'in' sensor before the membrane, and the 'out' after the membrane. That will give you the rejection. If it's less than 96%, change the membranes. Put the sensors back where they were before testing membranes.

That may be good advice if you know the specifics of gis situation, but unless we do there is no way to know. He could end up at 96% with a brand new membrane. Many discount membranes only have a published value of 97%.

Dow and their 99% membrane states that is at 50psi with softened water with 250 incoming tds and 77degrees. This is why actually getting 99% is rare. Very few would have that scenario. If you are starting with a 97% membrane you could easily be at 96% or below with a brand new membrane depending on temp, incoming tds, types of dissolved solids in your specific water, water pressure, etc.
 

dhnguyen

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you really should get yourself a handheld TDS meter. They much more accurate and more versatile plus they're very inexpensive. I never bothered with the inline TDS meter.

That said RO membranes typically last about 5 years. If yours tested at around 20-30 for TDS it should be fine.
 

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