Will be watching this for sure bro, bet of luck!
I'd ask the experts to correct me if I am wrong here, but the way I understand it, it doesn't really matter what caused the rise in ppm, ie, epsom. That still contributes to your overall number, the same way it works when you use tap water instead of RO, or like myself, where my RO tank is getting contaminated some how. The only difference is you know what that 150 ppm is.
This is part of the reason hydro guys use RO water, start with the lowest ppm possible because every single ppm counts against you in your final number. I remember first hearing this and thought it was erroneous, of course I know it all right? lol. Learned real quick, yea that number counts against you. We are on a well, ppm 8-900 out of the ground. It was a big fail for me to try using this water untreated. I can't explain the science behind it, but I do know it's true.
Just some food for thought here bro and take it from a newbie hydro guy like myself, with a grain of caution, lots to learn.