Why is this plant wilting?

I just got these clones a few days ago and this one plant started to wilt yesterday. I thought maybe it could be the humidity, it was at 28%, so I put my humidifier in there and kept it at 50%. But its still wilting. The temperature has been getting to 90 degrees but I have an a/c in there to make sure it doesn't go over that. Anybody have any ideas?

looks like your over watering...

90 degrees is too hot IMO.

I actually thought it was too dry because the rockwool cube was pretty dry so I foliar sprayed it just before I took the picture.

Yeah, I've been turning on the a/c when it gets up to 90 degrees. I guess I need to get a timer thing where it turns the a/c on everytime it hits 90. The other plants are all fine.

Okay so I think I might know what it is. I just checked the water temps in the buckets and they are reading 30-31 degrees celsius. I know that's way too hot. How can I cool the resevoir down?

Nevermind, the plant is back to normal now. I just flushed it and put bottles of ice water in the resevoir. Thanks for all the replys.