New TDS meter, some issues - The Planted Tank Forum
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post #1 of 2 (permalink) Old 09-07-2012, 04:02 AM Thread Starter
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New TDS meter, some issues

I bough a new HM TDS3 meter. I have a TDS meter on my RO system and when I compare the 2 readings between them they are spot on.
I have extremlly hard water from the tap 450 TDS so out of the RO comes 11 TDS water. I start with a gallon of that and mix in GH booster to get 3 DGH which should be about 16.8 x 3 = 50 PPM plus the 11 I started with = 61 ppm. My TDS meter shows 126 PPM. Why is it off? I use the API GH test kit and it tells me I have 3 dGH.
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post #2 of 2 (permalink) Old 09-07-2012, 04:15 AM
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I thought GH only measured the cations. If you have 60 ppm of divalent cations and your GH booster is mostly sulfate salts, then you have 1:1 cations tlo anions. Then 120 ppm on TDS makes sense (60 ppm Ca2+/Mg2+, 60 ppm SO42-), as it is Total Dissolved Solids, not Positive Dissolved Solids.

However, I do not have a TDS meter myself. So do take whatever I say with a grain of salt.
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