i use well water,mine is 315 ppm and 7.2 ph,my system goes as follow
with seedlings and clones i buy bottle water and feed them ro water and the low number feed that is required for youth,as in 250 ppm,when i get the third set of true leaves i bump up my ec to around 300 ppm also transplant at this time,i feed them 300 ppm until they get there legs under them from the transplant,once they start to rock on,i start using my well water,i just add very little feed and let the plants enjoy the well water,thing is and your issue too i can almost garuntee is the limestone base aquifer, calcium,mine changes with the seasons too,so how i combat that with my veggie garden were i have no choice but use the well water is about every 6 weeks i add about 1/2 cup of ironite from garden center or home depot,the sulfur in it helps nutrilize some that calcium and controls the soil ph also,
for my weed i use ro water,i use cal mag with it,
i use well water i use no cal mag
for coco as i mentioned i start out with ro water and add the
calmag,that said i only use 150ppm of the cal mag leaving 100 ppm of food,coco always food never plain water,i know debatable,thats just how i roll.
once i have the plant ready to transplant ,i drop both ro water and
calmag