Put your hand above the highest bud on the plant and leave it there for 10 seconds if it is too hot then your light needs moving if not then it is fine.
Have you got a way of checking your PH? If it is below 5.8 it can cause problems and if left at a low ph over a period of time it will destroy leaves and eat the plant from the bottom upwards.
Also have you started to use any more nutes than usual? If you have that could be a problem. Drop down to half strength next feed and see if that helps.
Thats all i can suggest without the pics dude