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Help...Again


onux20

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Tank still not looking "right". I have been working on Ca and Alk trying to keep that stable. Some positive results but not as good as I'd hoped for. I know...patience.

 

So I decide to see what my TDS meter is reading. It reads 180 on the inlet, 60 out. Here is the question, all of the filters are about 4 months old...maybe 500gal. After running my old filters for over a year, I am surprised to see my TDS so high so fast.

 

Also, the color changing DI resin is about 50-50. should I change that out or let it ride? I have a refill I just dont want to waste it.

 

Any ideas?

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If the membrane isn't the issue per the previous post, here's a thought.

 

Are you using a hand-held TDS meter or in-line? What gpd membrane are you using?

 

If you have hand-held unit, you can test the various places along the line to see what's going on. You say TDS in is 180. Depending on your membrane, you should be reducing TDS 90-98%. You can check by disconnecting the line into the DI chamber and allowing the water to flow into a clean, dry cup to measure with the hand-held. With your input level of 180, you should be getting readings of 4 to 18 for TDS. Also note, once DI becomes exhausted (color change is not that accurate) it can leach TDS back into the water such that you get higher levels.

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I usually go for no greater than 10% on TDS. If it's 200, then 20 ppm or less works for me. I regularly change prefilters and carbon cartridges first as they are the cheapest and go from there.

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(edited)

Check out this post and see if it solves your problem:http://www.wamas.org/forums/topic/38447-rodi-membrane-seals-can-fail-alow-tds-to-go-up/page__p__329060__fromsearch__1entry329060Bruce

 

Checked out the seal. It looked good. Thanks tho.

 

If the membrane isn't the issue per the previous post, here's a thought.Are you using a hand-held TDS meter or in-line? What gpd membrane are you using?If you have hand-held unit, you can test the various places along the line to see what's going on. You say TDS in is 180. Depending on your membrane, you should be reducing TDS 90-98%. You can check by disconnecting the line into the DI chamber and allowing the water to flow into a clean, dry cup to measure with the hand-held. With your input level of 180, you should be getting readings of 4 to 18 for TDS. Also note, once DI becomes exhausted (color change is not that accurate) it can leach TDS back into the water such that you get higher levels.

 

Dont have a hand held. 35 gpd. Gonna due the filters first. If reading is still high I will change out the resin. Thanks.

 

I usually go for no greater than 10% on TDS. If it's 200, then 20 ppm or less works for me. I regularly change prefilters and carbon cartridges first as they are the cheapest and go from there.

Gonna start here then move on to di resin then new TFC.

Thanks.

Edited by onux20
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In general, your prefilters aren't going to affect TDS too much. In some situations, they somehow even increase TDS. I forget the exact reason but I have this happen myself. Yes they will take out sediment and big things but I'm not convinced these are the kind of things a TDS meter actually detects. Carbon won't decrease your TDS and if anything, when the sediment filters need changing, they are clogged and doing a better than normal job of filtering out stuff. Now if they truly are clogged, what they do cause is a drop in pressure to your membrane. That is really the place you need to look closely at.

 

Look at your membrane and see what it's PSI rating is. Try and figure out if you are close to that. Normal house pressure is around 40-50PSI. Many membranes operate at 65PSI. Under-pressuring your membrane will prevent it from working properly- causing a decrease in GPD output AND increase in TDS output. Measure the PSI going into the membrane as well as the TDS going out. If the PSI is too low, you really need to address that. If the PSI is in the required range, calculate the percentage of TDS out/in and see if that is in the specified range. Many membranes operate at 95%-98% rejection rate. So if your TDS going to the membrane is 300 and your output is 15, the membrane is working fine. If it's 100, you got a problem.

 

Changing the DI is only a band-aid. It can get zero TDS even if the membrane is putting out 100 TDS water. The resin just won't last very long and you'll spend lots of money replacing that often. You can get some specs and figure out how many gallons your DI should last for based on the TDS of the water going in.

 

The house pressure and membrane is the real trick. Think of it this way- the 50, 100 and 150GPD membranes all cost the same so why doesn't everyone get the 150? Well the 150 requires 65PSI water pressure. Otherwise is sucks. The 100GPD functions at lower pressures like 45PSI. But it's best rejection is only 90%. The 50GPD generally operates at the lower pressures and still achieves a 95% rejection rate. So basically, people who have higher water pressure or are willing to get a booster pump go with the 150GPD and those who don't get the 50. No one really gets the 100 as it's the worse of both worlds.

 

I describe all this stuff from experience. The TDS of my water from the tap is 180. After the prefilter and carbon block, it's 200. Out of the RO it used to be 40. My 150GPD membrane was only achieving 80% rejection and 50GPD. Turns out my water pressure was 40PSI. My water after the DI was 0 and the resin lasted for less than 100 gallons. Once I put a booster pump on it, I got 150GPD, 97% rejection and my DI is lasting many times longer. I'll recoup the cost of the booster pump in less than a year through saved DI changes.

 

Hope this helps.

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Thanks all for the input and advice. All i did was pull the TFC and reseat it. So far TDS meter reads 0. I will keep checking it to make sure it stays there.

 

My inlet PSI is just in to the "green" zone" ~40psi.

 

Thanks again.

Ron

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