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#1
08/27/2007, 11:49 PM
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RO/DI Guru Question
I have a 60 GPD Spectrapure RO/DI. I recently replaced the pre-filter (.5 micron), the carbon filter (.5 micron), and the DI cartdridge (last month). I will soon be replacing the RO membrane. I routinely test my output water with a TDS meter that has also recently been calibrated. Tonight, I tested both my input and my rejection water. Do these TDS readings make sense?
Input water: 118 RO Rejection Water: 174 DI Output: 000 How can the rejection line read more TDS than is going in?!? Am I missing something here? Thanks for any insight. |
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#2
08/28/2007, 12:05 AM
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the rejection water is more concentrated in TDS because some of the water has been removed from it to produce the filtrate.
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#3
08/28/2007, 12:06 AM
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You are correct. The rejection, waste or flush water will be 20 to 25% higher than the tap water at a normal waste ratio. Don't concern yourself with the waste but test the tap, RO only before DI and combined RO/DI. The RO should be about 98% less than the tap and the DI should be 0. If your tap water is 118 you will see 2 to 4 from the RO if its working correctly. If you have a SpectraSelect hand tested membrane it will be less than that. My Spectrapure Select gives me an RO only TDS of between 5.3 and 6.4 with a tap water TDS of 800 to 850. Much better than 98% rejection.
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Linear Mode
