green curling leaves (pic)

This started a couple weeks ago and is affecting all of the growth on just one lady among others with the exact care/environment. Everything looks nice and healthy other than the curling on all the leaf tips. No burning, just curling. Some are upside-down cupping, but nothing is too severe, yet.

70's-low 80's day/night, 400w mh @ 12-15" from top, nutrients don't seem to be an issue, but could be wrong. Using straight water for the next few feedings. Didn't do a soil test yet.

Excuse me if this has been posted a zillion times here, but since the symptoms are so similar to many problems I thought a pic might help be pretty specific as to what's going on.

Ideas? Thanks.

any takers?

it could be root bound

i had the same problem in hdro and found that it was just a strain trait, it didnt hinder the plant at all. If everything looks healthy then i think your in the clear.

hey man i have the exact same problem, bright green leaves but the tips are curling downward, to be honest with you it didnt happen until i gave it its first batch of general hydro micro grow and bloom treatment, but other than that im just giving it 1tsp of grow and micro in one gallon of water, then just giving 200ml every third week.

once a week about a half a quart, how often should i water, and how much nutrient as far as the gh micro grow bloom, im soil based by the way

i mean this is my first time growing

i have 4 plants under a 250w mh with agrosun gold bulb w/ red spectrum. watering about a half of a quart per week per plant, giving nutrients of grow and micro 1 tsp per gallon mix, once a month, how does that sound, about right