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Discussion Starter · #1 ·
Hi,

I'm having trouble with a RO installation. My TDS is reading at around 70. I have tried 2 different RO membranes and 2 different filter housings (different brands0. I have a whole house filter and TDS going into the RO filter is 350 ppm. Also, I have a pressure regulator, and I have dialed the pressure all the way to 60+ psi with no effect on the TDS.

I have inserted, re-inserted my membranes many times. I wonder if the waste water is by-passing into the permeate water outlet via the o-rings. Should they always be lubricated? Re-inserting the membrane seems to change the ppm which made me wonder about this.

Any insights would be appreciated.

Thanks very much!
 

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Welcome to TRT :wavey:

I'm not your guy for the answer to your problem. Look for a response from AZdessertrat who is the expert. Some things you may be asked though is what system are you using, what is the membrane rated rejection rate, is it RO only or RO/DI, what is the ratio of RO to waste water, what type of whole house filter, and what are you using to measure TDS?
 

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Discussion Starter · #3 ·
Thanks for the questions. I should have clarified those earlier
Both membranes are rated at 98% (one is Axeon, another one is a Korean brand CSI). It is a RO system only. The whole house filter is a carbon/KDF-55 multi-layer system to take out chlorine and heavy metals. There is also a water-softener in the path. I'm using regular sodium chloride crystals.


I'm measuring the TDS with a HM digital meter. I have checked against store bought DI water and my own distilled water that I make at home and the readings are within 0 -5 ppm. I don't think the meter is off.

Also, the system did have readings of ~20 ppm after an alkaline filter sometime back. So things were working fine before. The problem started when the softener had a hiccup and overflowed the salt. This caused the RO system to become extremely salty showing a ppm of ~160 ppm (Should this even happen? Does that mean, there was a leak always?). Ever since then, I have been trying to swap out filters and recover the system but no luck getting the ppm down.

I have experimented with multiple flow restrictors (250, 400, 550 ml) and different pressure settings. Nothing seems to get the pps down. My only guess is if there is a micro-leak in the o-rings (and I got unlucky with 2 membranes and 2 filter housings?). It doesn't seems like a regular practise to apply lubricant to the bottom o-rings on the filter. But that looks like my next step.

Thanks again for any pointers.
 

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Discussion Starter · #6 ·
Tap -> Wholehouse water filter -> softener-> RO system

Ro system;

1 micron filter -> carbon -. carbon -> RO membrane -> permeate pump
 

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Discussion Starter · #7 ·
Just to note, I measured the pressure to 60 psi+ going into the inlet of the RO filter housing. I have played with all parameters. I just haven't tried the silicone lubricant on the bottom o-rings. Some installation procedures seem to recommend doing that ; most others don't.
 

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Sounds like your membrane and/or your housing is not the standard Dow Filmtec 1812 configuration. Some systems such as Sears, Whirlpool and some Watts Premier use a slightly different membrane that is hard to tell apart if you are not sure what you are looking at.

Do you have any photos of how the unit is plumbed? It is very easy to plumb one wrong, done it myself many times when I was in a hurry. Each line has a very specific location it must go and it is usually the end of the membrane housing with two lines going in and out that is the culprit.
 

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Discussion Starter · #9 ·
I will attempt to post photos in a bit.

Are you suggesting that I got the drain outlet and the permeate output on the filter housing mixed up? I definitely think I have that right.

The TDS on the drain port is around 250-300 indicating that the RO membrane is filtering something to get to a TDS of 60-70 on the permeate port. The total TDS adds up to the one at the inlet.

The filter is sitting flush in the housing. I'm not sure how to tell if the o-rings are not snug enough that they are mixing product water with the brine. That seems to be the only option I haven't explored. Thats why I was asking the bottom orings need extra sealants.

Thanks again!
 

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You stated in your original post that the incoming tap TDS is 350. If you are measuring the waste TDS at only 250-300 you are plumbed incorrectly. A normal RO membrane runs at about 4:1 waste ratio meaning the TDS in that one good treated gallon of RO water is concentrated in 4 gallons or brine or waste which is what flushes the RO membrane and keeps it usable. That means your waste will be 20% to 25% higher than the tap was to begin with or more like 420-450 TDS, not 250-300.
Post the pics, especially the plumbing and locations of the lines in and out of each component. Something is wrong for sure.
You also say you have a permeate pump, so does that mean you are taking TDS readings out of the pressure tank the permeate pump fills? This is not a good idea since pressure tanks contribute to and store TDS creep water.
What is your tap water TDS, RO only TDS directly as it exits the RO membrane not from a pressure tank or storage vessel of any kind, your water pressure and your water temperature? What is your exact measured waste ratio using a measuring cup and clock or watch for exactly one minute on the waste line then from the treated line?
 

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Discussion Starter · #11 ·
My plumbing in the picture below (pls ignore my older ro unit in the background). Orange tube is the feed from the 3-stage filter to the RO; pressure is > 55 psi.

I got another new membrane. Still no good. There is no tank in place now.

Incoming water tds is 360, brine is 410ppm, and permeate water is 57 ppm.
Can't see what I'm doing wrong. I did try without the permeate pump before; that didn't change the tds either.

The waste water ratio is well over 6:1; I'm using a 550ml flow restrictor
 

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Two things I can suggest. One is make sure the membrane is inserted all the way in the housing, it goes in further than you think, past flush with the end. The other is remove the permeate pump, they do absolutely nothing without a pressure tank to drive them.
On a side note, exactly what membrane do you have and is it rated at 96-98% sustained rejection rate or is it rated at 90% rejection rate like the Dow 100 GPD is?

How and where are you testing the TDS? If you suspect issues with your system, make sure to test directly from the tubing or source and not from a storage vessel. First I would make sure you have a fresh gallon jug of distilled water and a squeaky clean, clear glass drinking watre glass washed by hand in extremely hot water so it has no dishwasher soap residue or antispotting agent films on the glass to skew readings. Check that a glass of distilled is in fact 0 TDS. Draw a glass of tap water and insert the meter letting the reading stabilize and write it down. Triple rinse the glass and meter in distilled water, remove the white tube from the RO membrane to the permeate pump at the pump and let the system run at least 5-10 minutes then draw a sample of RO only water from that point, insert the meter, let it stabilize and write it down. triple rinse the glass and meter in distilled wate rand if you really want to take a sample of the brine or waste and again triple rinse the glass and meter in distilled, cap the meter and turn the glass upside down so it stays clean for next time.
What are all those TDS readings?

Have you timed your waste and treated flows to see if it falls in the range it should? If you are making water faster than 50 or 75 or whatever GPD that is also an indication the membrane is not seated properly and water is bypassing.

A 75 GPD membrane at 77 degrees F and 50 psi should produce about 6.6 ounces or 195 mL per minute. Both water temperature and pressure affect this amount so you need to know exactly what those are, not just a range or guess.
 
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