Did you keep the plants in the same containers? That's the only way to know for sure if the light is the problem. If you swithed reserviors too we still don't know for sure if it's light or nutes. Personally, I'm leaning toward a nute problem. If the temps are below 80 your light cannot be too hot.

When my plants are the size of yours I have had my HID light close to them for several days. You just need to wean them into the intense HID light over a period of about two or three days.

Root reservior should be completely light proof, just like in nature. This is not imperative however. A little light won't hurt, but you want mostly dark. Not only for the plants sanity, but to reduce scum and algea buildup.

Glad to hear they are improving.