OK, so I posted earlier about trying to dry my probe for calibration, but this is basically a different issue, so I figured I'd start a new thread.
I got my conductivity calibration fluid a few minutes... pinpoint brand, 53mS. Went through the whole calibration process... probe showed 34.9PPT in the fluid after calibration, so I stuck the probe in the tank... it immediately dropped to 32PPT. I know the tank is at 35PPT because I just calibrated my hydrometer yesterday. So I go through the calibration process a second time with the same results... 34.9PPT in the solution... 32PPT in the tank. I tried to take a cup of tank water and test that in case there was stray voltage in the tank... still 32PPT. Put the probe back in the solution and it goes back up to 34.9
So as I'm sitting here pulling my hair out I grab the refractometer and figure I'll try to recalibrate that and test again just in case that reading was off and the water really isn't at 35PPT. As I was doing so, I happened to notice that my refractometer calibration solution says "35PPT Refractive Index Standard Solution", but below that it also says that it's 53mS. So I put a bit of that solution in a bag, get it up to temp in the tank and stick my conductivity probe in it and get a reading of 38PPT.
So at this point it looks like my two calibration fluids differ by about 3PPT and the question now is, which one do I believe? The one I just got today is pinpoint and the other is from Aqua Craft Products and I only got that a few days ago, so unless they had been sitting on the shelf for a long time at Amazon they should both be fresh.
Should I get a third fluid to try to test with? One of my LFS's sells a lot of Neptune stuff and they may have a packet of the Neptune solution on the shelf. I avoided that one because I figured that the 2oz bottle I got would last longer than a single packet, but at this point I'm thinking that I might need a third source.
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