Discoloration, bugs? nute-lockout? Just stress

Hi mate, as they are all showing the same symptoms roughly the same time. It is logical to assume its not a natural deficiency where they have been underfed. The looks more like a PH or root issue. Magnesium and calcium deficiencies are the first tell tale sign of a lockout. Fully check all PH levels and condition of root zone for slimy or dark roots. Soil is very forgiving but it may be worth adding a tsp/ltr of gypsum/water (PH 6-6.3). This will act as a great PH stabiliser. Also epsom salts will give her Magnesium, adding 1/4 tsp to ltr of water and using as a foliar spray just as lights go out or just as light come on. I hope this helps, good luck and happy growing.