July 30: these plants are not thriving and it seems to be due to high pH soil. Runoff pH monitored during watering today was well over 8 which is way too high. This is due to last year’s use of high Na well water. Therefore the real problem is too much sodium on the cation exchange sites in the soil.
To fix i flushed with 10 L of pH = low 6ish RO water (50 ppm) and then 15 L of high Ca (from gypsum) and high Mg (from Epsom salts) water to push the Na off of the exchange sites on the soil and into the water. Monitoring pH and TDS in runoff and stopped when pH in runoff dropped below 7.
Fixing this takes a lot of time and effort and water. Glad I noticed it early and replaced most soil for the main crop. Last 50 bags had this B grade soil mix with too much Na that I was hoping to get away with. Damnit.