Mine is their TDSTestr Low, which is still pretty basic. All I know is that I've been using the same GH calibration and calibrating it to 1500ppm. If it's really a 0.7 conversion, that explains a lot.

I've mainly been seeing Mg deficiencies in mid-late flowering. I'm using the Lucas formula, and I know Lucas has stated that the Mg deficit is usually the first to show when your concentrations aren't high enough, since the formula has *just* enough Mg for the needs of the plant. The LF recommends a nute concentration of ~950ppm @0.5, and ~1330ppm @0.7. I had my white widows on my most recent grow running between 1050 and 1100 (on my meter, whatever it actually is lol) throughout almost the entire grow, and WW is supposed to be fairly nute sensitive. If my meter is really a 0.7 conversion, that explains why my widows liked the concentration so "high".
Help_Needed Reviewed by Help_Needed on . TDS Meter Calibration Issues I'm hoping that there are some really smart folks out there that can help me understand something of the world of meter calibration. After making my purchase of an Oakton TDSTestr11, I asked the young genius behind the counter for an appropriate calibration solution, for which he hands me General Hydroponics Standard Calibration Solution. Here's where the confusion starts, as the package indicates that it calibrates to 1500ppm (NaCl), 2190ppm (442), and 2930S (microSiemens). So everything Rating: 5