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Unread 01/15/2019, 10:39 PM   #1
john08007
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When do I replace my RO/prefilters

I've had my RODI filter running for several years and never replaced anything. Just checked my in-line tds meter, says 130ppm on input, 5ppm on output. I figure after several years it's time to swap the 3 prestige filters. Should I also change the membrane? The DISTRICT resin still appears to be the original color. Does the 5ppm indicate the membrane is bad?


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Unread 01/15/2019, 11:32 PM   #2
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Quote:
Originally Posted by john08007 View Post
I've had my RODI filter running for several years and never replaced anything. Just checked my in-line tds meter, says 130ppm on input, 5ppm on output. I figure after several years it's time to swap the 3 prestige filters. Should I also change the membrane? The DISTRICT resin still appears to be the original color. Does the 5ppm indicate the membrane is bad?
Typically, the sediment filter is changed when there's a pressure drop at the guage prior to the RO membranes. I used total chloride test strips for my solid activated carbon cartridge. If the reading ever starts showing something I'll know that its adsorbed enough organics to reduce its effectiveness to deal with chlorine/chloramine.


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Unread 01/16/2019, 12:24 AM   #3
bertoni
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I would check the TDS just before and after the membrane. The membrane probably is fine. I can't guess how much life is left in the DI resin, but I wouldn't expect much, not in the average situation, anyway.


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Unread 01/16/2019, 05:41 AM   #4
mcgyvr
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While clearly there is wiggle room as shown by the fact you have ignored maintenance for years now...... Typically something like the following applies..


When the rejection rate of the membrane drops below its specification its time to change the RO membrane.. Usually something like when it drops below ~93-95%. That usually takes like 3-5 years

You change out the prefilters when the pressure drop is high enough that its causing the pressure at the inlet of the membrane to be too low.. That may be in as little as 6 months and typically not longer than 1 year based on usage/water quality,etc...

You change DI resin when the TDS output is not zero.. Usually that means change it about the same time as you change your prefilters..


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Unread 01/16/2019, 06:11 PM   #5
john08007
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So, seems like i should upgrade my setup to include 2 pressure gauges, before prefilters, and between prefilters and ro membrane?


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Unread 01/16/2019, 07:15 PM   #6
mcgyvr
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So, seems like i should upgrade my setup to include 2 pressure gauges, before prefilters, and between prefilters and ro membrane?
That wouldnt be a bad idea at all..


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Unread 01/22/2019, 12:24 PM   #7
laverda
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Your luckly the TDS of your incoming water is so low. That is probably why you have been able to get so many years out of your system with out maintenance. My TDS is well over 3 to start and 5 & 7 coming out of my duel membranes. One pressure gauge at the membrane is really sufficient. You just need to watch for it dropping over time. In your case I would think the carbon block should be replaced before you will see a pressure drop in the gauge. If you at 5 ppm out of you membrane that is high depending on the rejection rate of your membrane. If it is 5 ppm out of you DI then what is coming out of your membrane is probably higher still and your DI needs to be replaced. Either way your DI needs to be replaced. Idealy your TDS should be zero out of your DI. Many people replace as soon as it shows 1. Personally I let mine go to 3 TDS before replacing it. The pre filters are cheap and are there primarily to protect the membrane from getting clogged by larger particulate mater and from getting destroyed by chlorine. Chlorine & chlorimine will damage your membrane quickly. Testing for chlorine after the carbon block occasionally will tell you when it needs replacing. At this point I think you need to change everything. In the future change you pre filters more frequently and your membrane will last longer. How often you need to change is very hard to say as there are so many variables. The amount of water you make, the amount of chlorine or worse chlorimine in you tap water are the biggest factors to consider.


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