Fan Leaves Curling up

I have four plants under a 400 watt hps bulb. They are all about the same size, so I would think if it was due to being burnt by the light, that is not the case. No yellowing of leaves, no discoloration, no diseases that I can tell... the leaves just seem to not flatten out. They are curled up like a blunt. Should I be concerned? Or will this simply not matter in the end? I am also feeding all four plants the exact same nutrients (flora micro) and I only have one Bubblegum strand that is giving me problems. It's about 2 feet tall at the moment. Only thing I can take a hint at is that their container is too small. But if that was the case, wouldn't all of my plants be suffering the side effects? Any suggestions? Help please. First time medicinal grower.

What is the pH of your soil and your water? If your pH is below 6.5, you are probably getting Magnesium lockout which would cause the leaves to 'taco' or curl up like you are describing. Measure your pH first, so you can fix that before you do anything else.

Also, if you think your containers are too small, you should go ahead and transplant into bigger pots. How tall are your plants and how big are their containers?