Tips curling upwards and turning very dark

I dont know whats going on with these clones. They have been on 24 hour light and the buckets are being ran 1hr on 1hr off all the time. Some of the water has been filtered through a brita water purifier. Is this bad for the plant? does it take away important stuff in the water? anyways they been like this for a couple days one of the two is pretty prevalent and the other only has it on one or two leaves.

more shots o yeah strain is white widow x sour diesel. theres a shot of a flowering bag seed plant that also looks like crap pretty sure its nute burn but but tell me if you think otherwise. Maybe it has to do with the brita.

Does anybody have any Idea I cant find anything that looks like this around here.

curling most likely ph imbalance or nute burn. check ph first.

Ph is fine. been checking and maintaining that. Nutes are GH mixed at ~ 40% 24hours of cfl light.

Any other ideas? do you think the nutes are too strong for a clone that has been rooted. Roots are even in the resevoir allready and the plant is probably ten inches tall.

does nobody have any idea? I'll put up some better pics tonight.

i had something similar and it was nute burn i flushed them and they got to normal