This is my first grow and would like to know if this looks like heat stress from getting too close to the lights or a nute deficiency. They are lowryder #2, day 23. Its bubbleponic system in a dr60 tent with 126w Penetrator LED from hydro-gro and two 13w CFLs. Its well ventilated with can fan 164cfm on a controller and carbon filter. Water in the res is around 68-70F and the air temp at the plant tops is 77-81F with lights on, humidity is around 55%. I have been running the lucas formula with nutes at 1330ppm for a while and no problems till now. My girls experienced some rapid growth and got to be around 4" from the light, I don't know for how long exactly (8-12hrs maybe). Its only yellow at the tips that were closest to the light; there is no other discoloration anywhere on the plants. Thanks for your help.
Thanks for the input. I had some problems at first with res temp and slimy roots, but i solved the problem with a homemade water chiller. As a result two of the three of the plants are very undersized. So, I would say one plant takes up about 70% of what you see.