Doing outdoor organic grow, healthy all year until about a month ago, after too dress plants looked much worse. May be my hard water but I have no clue now

looks like some Ca deficiency (rust spots without interveinal chlorosis). N deficiency working its way up the plant. if the pots are not buried in teh ground, treat it like a potted outdoor plant. that means some of those top dress options are a bit danagerous to use if you don't have the dose correct for that small volume of substrate. Vs. in the ground it will be spread out and more easily used at better concentrations. trial and error to get your ratios right. how frequently you top dress or fertilize will impact how concentrated it should be... over time a 'good' concentration will add as many grams of NPK et al to soil as anything else that works well. wether you fertilize 1/week or 1/day etc... though more freuently with lower concentrations does promote faster growth. whether that is important to you depends. it's also more work. outdoor, more frequent fertigation may not be as beneficial as it is indoors.

Pictures 1 & 2 are showing a plant in stress the other pics look ok for this point in the season, you’ll see more yellow leaves as the plants are flowering & the foliage begins to die, pick off those leaves as they turn brown. Back to the stressed plant, I can’t tell what is the cause but the twisty leaves kind of indicate a possible excess or possible disease😬 Since you’re in small bags I would get that plant segregated so if you’re dealing with a contagious disease it’s not continuing to spread. Go clean up after moving it, do not go back and handle the other plants until you can be certain you are not the vector for this. Watch the stressed plant for further decline (toss it in the trash if it gets worse) or if it somehow improves keep an eye on it. Cannabis like every other plant on the planet can / will occasionally have problems that are often caused by their human partners but overall it looks like you’re doing ok other than the one

I also just flushed medium with RO water last week because I thought the hard water may be locking out potassium because of calcium in the well water. Soil was mixed and cooked with all nutrients in 10 gal. I started seeing yellowing about 5 weeks after transplant into 10Gal pot so I top dressed and it lead me up to this point