Leaves starting to droop and show signs of stress

Took a look at your diary cause I needed to see how far your grow was. 1 thing caught my eye right away, I've grown in dwc before, 6.2 ph my friend was the best sweet spot for me. I think you could be locking out nutrients from your plant as certain nutrients are only uptaken at 6.2 and above example calcium and magnesium. I would first correctly my ph in any grow set up before worrying about ppm. Plants are very very troublesome in hydro as they tell you immediately what they need and when, you supply it and they're golden, you dont and problems will continue. Try correcting ph first and see if it helps. Happy growing bud

It depends how far into the grow you are. In late stages of flower, yellowing is normal, if its still early on, it could be excess nutrients