Leaves curling down and cupping

These plants are one month and 9 days old and the edges of the leaves are curling upwards cupping the leaf slightly. This has been happening for about 2 weeks and now on some of them the leaves are curling down. I am using organic soil that has a good drainage and i water about every other day when i see them get droopy and the top layer of the soil is dry. I am feeding them Pure Blend nutes and they are under a 400 watt mh with a bowl of water for humidity.
I thought that maybe the bowl of water had something to do with it but when I removed it for a week or so no progress was made so I put it back in. They are on a 24 hour light schedule too.

If anybody can help that would be awesome. This is my first grow and I don't want it to go to shit haha.

Thanks

I have the same thing going but my tips are curling down someone told me it was too much nitrogen but I dont know if thats your problem but your serrations look the same as mine so it might be something to consider. I honestly think its a transpiration thing like moisture is leaving the leaves so the cells are becoming smaller on the surface causing it to cup.