in the tips could be heat or nutes.
are you monitoring temps indoors? have you possibly overdone it with ferts in the soil or watering schedule? are you watering with plain water in between? etc, need more info to help..
I just moved a plant from veg into flowering and the hps made the tips burn, for example. But I have another plant in the same room, who is used to the heat, and has some burnt tips from when I over did it with fertilizer.. If its fertilizer, flush the plant with distilled water and check the run off ph. Otherwise, its probably heat. Keep air moving and cool the space or the lights if possible
well if you started with a good rich soil you might not even need nutes early on. I plant in Fox Farm and my plants didn't show signs of needing nutes until 4 weeks into veg. Same goes after transplanting, because there are more nutrients available in new rich soils..
did you not flush when you switched nutrients to flowering from veg. this is essential as the flower nutes are thrown way out of balance by the left over properties of the veg oriented soil