TDS 1 with DI
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Ty Hamatake
Hi, my name is Ty and I'm a Reefer...
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What's your PSI at? I'm pretty sure that has some affect on the efficiency of an RO membrane, and the more that gets through the membrane, the more that gets through you resin. It could also be a faulty meter. Do you have a way to double check the TDS of the product water?
jsker
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A good pressure for a RO system is 65 pound of pressure and the more pressure the better. Also check your local water supplier and see if the utility is using chloramines. Most do, to extend the life of processed water and the process will raise the TDS before the DI unless one adds a double active carbon filter before the membrane.
A good pressure for a RO system is 65 pound of pressure and the more pressure the better. Also check your local water supplier and see if the utility is using chloramines. Most do, to extend the life of processed water and the process will raise the TDS before the DI unless one adds a double active carbon filter before the membrane.
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Are you measuring inline, or later with a hand held meter?
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The reason I mention it is even CO2 from the air can boost the TDS to about 1 ppm.
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I think you'll benefit from higher PSI, but a DI should get to 0 ppm TDS even without an RO membrane at all, assuming it is working perfectly.
It could also be as simple as improperly calibrated TDS meters. In-line are supposed to be calibrated with the water flowing through - which I have no idea how to accomplish that with the calibration solution. The in-line meters have a VERY sensitive calibration screw as well.
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The inline meters I used were not able to be calibrated. 
The inline meters I used were not able to be calibrated.
Really? Even the cheap, ubiquitous HM digital meters that BRS sells are able to be calibrated. If I remember correctly (while typing at work), the older ones needed to be popped open to access the screw, and the newer ones have an access hole on the back case...or maybe it's vice versa.
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I used the inline meters that came with my Spectrapure systems. Possibly I could have taken it apart to recalibrate, but I couldn't see any reason to even try. IMO, good calibration is not needed if the goal is to ensure 0 ppm TDS water. The zero point doesn't move on calibration, only the slope.
Maybe I am missing you here...are you saying that, for example, if I have the 341ppm(?) standard calibration solution for HM meters, and the meter reads, say, 600ppm, that it will still read 0ppm at true zero?
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Yes, calibration of a TDS meter (or any conductivity meter) only changes the slope. That's why only one calibration adjustment can be made on any conductivity meter (if any). If you could change both the zero point and the slope, there would be two adjustments, but zero is zero in this case.
Yes, calibration of a TDS meter (or any conductivity meter) only changes the slope. That's why only one calibration adjustment can be made on any conductivity meter (if any). If you could change both the zero point and the slope, there would be two adjustments, but zero is zero in this case.
I'm glad I wasted time and money on this!
