Does it come with a calibration source liquid? Do I need to buy a meter with one or can you easily make your own?
This one have a calibrated potentiometer in the back with label "Calibrate with NaCl".
I'm sure you can get calibration solution online and just adjust the pot in the back. For $17, it do not come with the solution.
TDS can change from time to time and i dont think there is any calc for it.
my tank water read .5KH and 5GH 5x17= 85tds and the tds increases by it self or after dosing some ferts but 5Gh remain the same or become 6Gh if am dosing Ca and Mg, right now tds is reading 200ppm+ with the meter but API reads 6dgh