I've got some Sadhu and these Thai X Skunk freebies growing together. The Sadhu do not show the leaf curl and the ThaiSkunk do show it. I was using tap water which is pretty hard around here and it was causing some problems. But now I am using distilled water corrected to about pH 6. I am struggling with temperature which has drifted into the nineties and is never below the low eighties. I had a little emergency one morning where I caught the tops drooping over after putting in a new HPS 250Watt, but that was very recent and they recovered right away as soon as a moved them away from the lamp. I also wonder if overwatering were a problem, I keep the water meter over 2 and generally into 3. And the Sadhu get the exact same watering treatment. I do notice that the Sadhu to keep the soil moister than these Thai crosses. Maybe the Thai cross is just using more water, in which case that might suggest, I am underwatering.
Here is what I am looking at:
I also found some other posts with similar problems. There are a lot of complaints about leaf curl, but I found only a few that looked like mine:
Go to the actual posts to get the full size images. This one looks exactly like mine,
http://www.gardenscure.com/420/plant...-question.html 
This is also pretty close,
http://www.gardenscure.com/420/plant...curl-help.html 
Here is another ThaiSkunk, but it doesn't look exactly like mine, the leaves are not curling up or twisting like mine are.
http://www.gardenscure.com/420/plant...leaf-curl.html 
Any idea what is going on? The heat is really a problem, I'm sure. There's nothing I can do about the heat. I'll never start a grow in late spring or early summer again around here.
So what is going on? The clues at the other posts weren't much help. Twice it was suggested that it was overwatering. Both posters objected that it couldn't be that. But overwatering can be a problem. I thought I was overwatering and it turned out that it was just the hard water that was burning my plants. But that could be it, I could still be overwatering.
Any and all tips or clues would be appreciated.
And here is search for anyone else looking for "curl" in the nursury:
http://www.gardenscure.com/420/searc...=1140279&pp=25