4 week old plant is curling on the edges of its leaves

sitting under 400w MH bulb 4 weeks in and only one is effected I have two of this same strain the other one is fine it's just this one that is curling up on the edges of its leaves. the RH in the day time is around 30-35% at night it goes up to about 40-45%. The temperature is at 80-81F every day, at night time it drops to 60-70F. I was thinking heat stress or low humidity that would be great if I can get some tips to fix this issue thanks

Looks good to me, you could probably bring up the nitrogen levels a bit. The hint of the yellowing could be fast growth that is normal or it could be lack of N. But nice plants, I wouldnt worry about it.

alright thanks and yea it's growing real fast that could be it I don't think it has a n def because I'm feeding them once every 3 waters using sensi grow part a and b advance nutes

Looks like heat stress the way the leaves are rolling in. Pick up your light a bit. Humidity may be a bit low a damp towel or pan of water might help (never had low humidity problems just the opposite where I live) The yellowing I wouldn't assume its nitrogen def. that starts at the bottom leaves and works its way up. More pics and info will help sort that out. how often you water and feed at what ppm