Thanks AZDesertRat, I know they are off because I have 3 coralife digital thermometers, and two kitchen liquid thermometers. The five all show the same reading within .2 degrees and the two HM meters show 3 degree difference (it's weird).
If the calibration of the HM PH Meter is off will it effect its thermometer calibration?
I bought these meters to make life a little simpler, but it's becoming more of a headache.
I bought a refractometer from Dr. Foster Smith (the blue model), and some calibration fluid. I calibrated the refractometer and thought it was good to go. A couple days later I tested it with the calibration fluid again and it was off. I screwed the screw all the way in, and it can't go any further, but it says it's still off by 1PPT (in the direction it needs to go).
The one meter I did buy and works great is the low range phosphate digital meter by Hanna. I have .02ppm of phosphate, yeah I think.