Curling leaves

I started this plant about a week and a half ago, under a 250 W MH and have not added any fertilizers yet and one of the two plants looks perfect while the other has curling leaves and decently dark leaves. Does anyone know what could be causing this curling???

check your ph. when i got to my brothers grow all the leaves were like that.The entire canopy was a dark green color. They had been watered from tap water with a ph between 7.5 and 8. the next water we gave them water at 6.3 to balance out the ph of the soil. within a day all new growth was light green. Within a week the entire canopy was perfect green. Now we keep it at 6.5-6.9 aiming for 6.7.

could be a deficiency but definitely start with ph

tap water should be fine to use with ph down.

if you would like to strive for perfection use a brita water filter or ideally an ro filter

Looks alright to me. Do you know the strain? I had one in my previous grow where all the leaves did that. I think there's a name for this curling. So, I pollinated a few buds of it, got seeds, grew it, and now I have one that looks the same. I was worried my grow conditions caused it somehow, so I cloned it a few times and BOTH clones do the same curling. Now don't quote me because I'm no expert, but I think it is a strain trait.

Ya it is feminized big bud, and ive been monitoring the ph and ive been keeping it around 6.5 -7 but i am gonna try it at 6.0 to see if it changes the plants and i have a PUR water filter on my sink so hopefully it will straighten itself out....

could be strain but i dont think so. probably a micro def. either way you shouldnt worry. your plants look beautiful and very healthy. in soil i wouldn't recommend going down to 6.0 unless you need to balance the ph of your soil. mine prefer 6.7.