The ppm or EC (same thing different system) of your well water is reading micro nutrients and not the NPK nutrients. You will need to be cautious that you have enough of these micros in your mix. When using Reverse osmosis filtered water you have nearly zero disolved solids. The nutrient manufacturers either cannot put enough micro nutes in their formula without locking of other nutes or they allow for some of these micros that are usually present in tap water. The main micros that are usually lacking are Calcium and Magnesium. Your water sounds like it may be OK but may be a little light on the Cal/Mag. My tap comes out very low at 33 ppm so I use a product called Cal-Mag to supplement the micros.
The earlier post was correct though you do not account for the ppms/ec present prior to adding nutes. I would try to do without Cal Mag and if you see any chlorosis or necrosis developing I would diagnosis it as a Cal/Mag defiecency as a first option.

Good luck and let us know how they are doing...



Peace and Love -Jay

Look for leaves doing this...