What is the pH of your soil and water? Cos it looks like a few things there mate, magnesium/calcium deficiency and they look a bit hot too (crinkly).
What light and how far away? Temps?
The more info the more chance someone can help! Check out this sticky anyway - it's good to have a comprehensive run down of problems.
For the watering i correct the PH from 7.0 to 6.5.
Also i should tell that my grow environnement can be somewhat hot, the temp sometimes increase at 40C.
For this reason i maintain the lamps at 20 inch for a 400W, could it be a overheating sign?