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Old 03-01-2004, 11:34 AM   #1
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How to deal with high TDS reading/

I installed my RO/DI system over the weekend. It is from filterdirect from ebay.
On Saturday, I check my TDS reading on the RO water and is reading about 11ppm. Knowing my tap water used to be 230ppm, I am pretty happy.
On Sunday morning, I dispense some RO/DI water and lo and behold I tested to be 19ppm??? Knowing that my RO/DI TDS should never be higher than my RO water, i retested my RO water and it turn out to be 20ppm? I retest my tap water and now it reads 350ppm!! I know my TDS is good and calibrated because I have a RO/UV water that I know is about 3ppm. I use my TDS meter to test that RO/UV and it is consistently reads 3ppm no matter how many time I test it.

Now, my question. Does the city water quality flunctuate all the time??? Does my DI resin need some time to kick in so that it is actually doing something? Even so, 20ppm at the RO is still high for my DI to get to 0ppm? So any solution. Add another RO/DI in series??
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Old 03-01-2004, 03:15 PM   #2
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Now, my question. Does the city water quality flunctuate all the time???
I honestly don't know, you would need to ask your water company. Are you sure your not on a well? That TDS seems high for treated water.

Did you let the RO run for a couple of hours prior to using the water? There are preservatives in the RO membrane as well as the DI (I suspect) that need to be flushed prior to using the water.

Not trying to talk down to you, but on my first RO unit I did this, are you sure them membrane is in there? I left mine out once and was stunned at how fast that sucker could make water, LOL. Also make sure the membrane is seated correctly.
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Old 03-01-2004, 03:20 PM   #3
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Oh yeah, at an RO dishcarge of 20ppm your DI should reduce the TDS to 1 or 0 after that.

Your getting a 94% rejection rate on your RO but only gettin 5% rejection rate on your DI.
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Old 03-02-2004, 12:11 AM   #4
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My city supplied water ranges from aprox 180 to over 230 tds. Depends on the day and time of day. My RO/DI is always 0 - 1. Anything higher turns out to be a dirty container
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Old 03-02-2004, 10:32 AM   #5
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I don't understand. If I am getting 20ppm on the RO, and wants the RO/DI to let says 1, then the DI rejection should be 95% right? (20-1)/20.

What is normally the rejection for DI Resin?

Also, talked to FilterDirect on this. He was saying that if you have a storage tank on the RO side, you need to limit your ball valve at the output of the DI so that the water flow from the storage tank being pressurize will not flow too quickly through the DI resin and limit its effectiveness.

I tried this by turning by ball valve at the output of the DI to nearly close to Off position such that water is trickling out very slowly. However, I got 12 at the TDS reading. So the rejection is only (20-12)/20 = 40%.

I re-test my tap water. It is still 350ppm???? I called the city water and they said that they don't have a requirement to test TDS. The last time they tested is in 1997, and it reads 500-550ppm!!!.
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Old 03-02-2004, 10:52 AM   #6
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What is normally the rejection for DI Resin?
Ususally it should be between 95-99%

Quote:
Also, talked to FilterDirect on this. He was saying that if you have a storage tank on the RO side, you need to limit your ball valve at the output of the DI so that the water flow from the storage tank being pressurize will not flow too quickly through the DI resin and limit its effectiveness.
This would make sense to me, slower flow through the DI would allow it to remove more TDS

Quote:
I tried this by turning by ball valve at the output of the DI to nearly close to Off position such that water is trickling out very slowly. However, I got 12 at the TDS reading. So the rejection is only (20-12)/20 = 40%.
Use a known measure of water and time it, make sure it is not producing more than it is rated for.

I receive my RO/DI from them today and will be installing it this afternoon, so I am very interested in this thread, please keep it updated, once I start producing some water, I will post my results as well.
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Old 03-02-2004, 02:31 PM   #7
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I thought something didn't make sense I just got my RO/DI w/booster pump assembly (anyone wanna come hook this sucker up for me?) and in the installation kit is two ball valves, one for the tank and one for the DI. Turn the ball valve off to the tank so it cannot push any water out while your making DI water, then you can run the ball valve on the DI wide open.
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Old 03-02-2004, 05:37 PM   #8
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There should be a check valve on the pressure tank to prevent water from back flowing through the DI chamber. There should be a float valve connected on the storage container that will signal a shut off solenoid. The shut off solenoid will kill the water on the supply side until there is a pressure drop either from the float valve or the pressure tank. If you are getting 12-15 TDS out of the RO, it should be 0-1 out of the DI. Water that has been sitting in the unit for a while will read higher. Let it run for about 5 minutes and then check it...that's the only way you'll get an accurate reading. If your RO membrane is putting out water at a higher TDS than 15 or so, you might want to add a second DI chamber to the unit to polish the water down to 0 TDS.
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Old 03-02-2004, 06:34 PM   #9
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There is no float valve in the tank, there is an auto shut off in the unit that should shut off the water when it reaches a certain pressure. I'm running a booster pump with mine, so I had to remove the auto shut off valve and hook the solenoid and the pressure switch in it's place. The way the unit is designed, I don't see how you could put a check valve into the DI to keep water in the tank from going through the DI. Only one line goes to the tank, it serves both in and out. In order to put a check valve on it....you would not get DI water at all or you wouldn't get tank water, one or the other. There is a ball valve attatched to the top of the tank, whhen you want to make DI water for the fish, simply turn the ball valve off and all you will get is fresh made RO/DI water. There is a check valve that prevents the DI water from back flowing into the RO.
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Old 03-02-2004, 06:46 PM   #10
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OK, I think I see what you're talking about. The way I would set that up is to have the line for the pressure tank tee off between the RO and the DI. That way, you have RO water going into the drinking water tank. There would be an inline check valve or a check valve at the pressure tank inlet so that RO water could only travel in. If there is only one line going into the pressure tank and it's serving as an in/out line, the check valve would need to be between the RO and the tee up to the faucet. The line coming out of the DI would go to the float valve in the DI water storage container. If this is open and the pressure tank is full, water would automatically flow through the DI into the storage container. The pressure switch for the booster pump should be set just below the cut off pressure for the shut off solenoid...that way, it kicks out just before the the solenoid shuts down the water supply. At least, that's how I'd set it up. 8O
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