I tried a search, but wasn't sure exactly where to post this. I have a HM digital EC/TDS/TEMP COM-100 ppm meter. I lost the manual, but not sure it would help anyway, becuase my question is: which setting do I use? It has NaCl (registering in PPM) or KCl that measure is some funky greek symbol that looks like a U with an S, then a 442 setting that measures in the same greek symbol. it also has NaCl measured in this symbol. it also has KCl measured in PPM. any idea which I should use? This might explain why my PPM's levels seems so high, when I'm following the nutrients mixing guides. Luckily, over the last year, I haven't had any plant issues, because I've kept it no higher than 1800 ppm, but normally, I would think that 1800 ppm would burn the plants. Any ideas?