I was going to say curling down would usually be over fertilizer but it looks more like a wilt...
Hydro or soil?
If its soil I would try maybe easing off on the fert until you see either yellowing or some improvement.
Flushing the soil could be an option.
If its Hydro then I have never done...
Thanks for the input, I did veg my last plants under CFL but they yellow'd, never grew beyond a few cm high and were definitely doomed to fail. I switched them to HPS and they took off immediately. The problem is, I also added ventilation and repotted in different soil at the same time so It...