We perspire, plants transpire. There's not enough roots to take up enough water to compensate for transpiration yet. Aim the fan on the light for now. Could be a little burnt from nutes too. Cell ph, sm screen so I can't see the pic that well, but definitely get the fan off them for a while
as it's causing faster evaporation. But keep it on the lights to keep temps from rising. Is that lava rock? I had a pH problem when I used that too. You may need to change your pH product to get it to stabilize. Untill you find something that stabilizes it, check & adjust daily. That's why I prefer soil, less fluctuation. Good luck!

~~~~~~~~~~PEACE!~~~~~~~~~