That is def a heat issue. If your humidity level is to low the leaves will dry and curl alot quicker as well. try keeping your temp down and spray the plants with just filtered water once or twice a day. Also watch your ppms, one of the biggest problem in hydro is overfeeding because the plants are given everything they need in a self contained environment, therefore minimal nutrients are needed to reach peak growth potential. Very very rarly do you see a underfed plant in dwc.
In smaller grow places wind burn can also be a factor. if you have any fans in the room close to the plants or blowing directly on it for extended periods of time. But for sure raise humidity levels until flowers and keep room temp down down down.