My first dwc grow mixed genetics

I'm not a hydro grower but from what I'm told you need to look at the roots and see if anything is off. Is there good aerating for dissolving oxygen, do they smell at all? are you using a enzyme product to help keep them clean and healthy? This looks a bit like a PH issues/calcium to me. are their large PH fluctuations happening? 5.8-5.9 in veg is good and then bump it up to 6.2-6.3 in flower. First step I would take is to calibrate your PH pen and go from there. Then smell and feel the roots that's a good indicator of health. Again I'm not a hydro grower, just guessing from what I have seen/heard. Good Luck!