They are in veg for few weeks. It only appears on one plant, it started before about a week ago on one top. So i tought it might be light/heat stress. I have 400w mh/cooltube, had it 30cm from tops or even closer, so i started to move the light up, but it didn't help.. It spreaded to more tops now. I didn't use any nutes, as soil is supposed to have enough for some time, so i just add nutes in flowering.. It also has planty of airflow and air movement in room.. I also recently fixed room temps, as i saw minimum as low as 15 degress celsius at night(17 at walls) and had 27 degress at lights on, but only for few days. Tought it might be a problem, but now night temps are around 17 and day temps around 24.. I think this bright green tips are starting to yellow.... Any help would be great.