Ok well, I've been using the same water as I have the other healthy plants, so I'm not sure if it's the ph. My tap water is close to 7 and I leave it out for 24 hours before using it. It just seems to be the smaller plants doing this. I have fed them nutes a few times now, so I guess this could be the problem. How long after feeding them just water should the leaves start looking normal?

They're under a 400W HPS at the moment, which is just over a foot above them. But this started happening when it was under a 125W envirolite and 3 CFL's. I'm not too bothered about these plants, but I'd like to know what caused them to curl to avoid similar problems in future grows.

Thanks again people. Peace.