My first few grows I was using coco, and what I would do was nutrient my 4 gallon water reservoir once a week, or when it ran out, which happened bi-weekly once they were in heavy flower. I started PH'ing when I was mixing the nutrients, but like you say it was climbing back up when it sat around. What I ended up doing was mixing nutrients once a week, but only PH'ing the jug I used to actually feed the plants. It meant having to adjust the PH on 3-5 jugs of water, instead of 1 reservoir, but I always knew I was putting in exactly the PH they wanted. I didn't have any problems with the salts dissipating or anything. I think at the worst they will fall out of solution and you'll end up with "stuff" on the bottom, but if you thoroughly mix it before each feeding you should be fine.
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Don't sweat the technique.
And honestly. My fuck ups turn to gold so much the thought of fuckin up don't even bother me. So I keep it auto when I'm stepping through a portal. I know that sounds strange but, strange beats normal.