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Old 09-14-2005, 04:26 PM   #1
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RO/DI Water Quality Issue

So, I've had my RO/DI system for about 5 months. I have a 110 gallon tank. I do 20% wc every other week, but it took 2 months for my cycle to finish so, I've done probably 6 water changes (total of about 120 gallons worth). I use it for top offs as well, so figure an average of 6-7 gallons a week for that...(total 120 gallons worth, let's say). That's about 240 gallons of water pumped through my RO/DI unit - roughly since I used tap to start my cycle. I'm getting PO4 readings from my RO water now and have noticed it is flowing noticably quicker than usually. Could it be possible that I already need to replace the filters, or could something else be wrong? I'm not too familiar with RO/DI units, but doesn't 240 gallons worth of water seem low to need a replacement filter???? I don't have a TDS meter so I'm not sure of exact readings but, it is outputting close to .5ppm of PO4. Seems quite high for RO/DI water.

Any help would be appreciated. I'm already battling PO4, now my top off and water changes are dumping it in.

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Old 09-14-2005, 09:53 PM   #2
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How often you need to replace filters will depend on how "bad" the tap water is. If your tap water is high in TDS then you could in theory expect to get 240 gallons or less out of the DI cartridge, it really depends on the quality coming out of the membrane...less TDS out of the membrane will equal longer DI life. Also, capacity membrane do you have? 50gpd, 100gpd...the higher rated membranes have a lower TDS rejection and will lead to shorter DI resin life.

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Old 09-14-2005, 11:25 PM   #3
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I have 100gpd. If I do need new DI resin, would quicker water flow (assuming that means less waste water) be a symptom of that? Seems odd that a 100gpd wouldn't make 3 day's worth of fresh water, even with high TDS. I realize they do not think literally someone will run 100gpd - but, I find it odd.

I did locate a lfs that will test my TDS both out of tap and out of the RO/DI.

Thanks for the help.
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Old 09-15-2005, 08:38 AM   #4
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You have a common problem IMO.
I have high po4 and nitrate in my tap so I run 2 DI cartridges and rotate them out.
Your other filters are probably fine and its just the DI that needs to be replaced.
I used to burn through resin after a few hundred gallons, I also got a booster pump which seems to help with filter life.
Not sure why you would get faster flow out of the unit? usually if the filter get old and clogged you get less flow.
Pick up a TDS meter there like $25 online, its a must have with a ro/di unit.
You can buy bulk resin and pack your own Di cartridges to save some big $$$.
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ro/di, water quality

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