Mine used to do exactly that. I read about tomato leaf curl being cause by too much watering I thought WTF? My plant is growing in water so what do I do? But then I realized that too much water keeps the roots from getting oxygen so I tried putting an airstone in my
nutrient solution. After about a week or so the leaves were completely normal and I hadn't done anything else. So in my case that was what fixed it. Hope you got your problem fixed by now.
Good luck.