Yellow Tips On Leaves

I think this is the start of your root zone issue. Temperature of the substrate may be too high. Up until recently I have always put it down to a little over feeding or as romi27 mentions, heat/light stress. However, I found some info from another grower about this and he mentioned that it could be root zone issues. Substrate too warm. I assume it is the same plant that is misbehaving. Makes sense in some ways as to how it has behaved since this question was posted. I am going against light stress as you other plants would be suffering from this too. I hope this helps in some way. Always learning myself. Good luck and happy growing

For me, it's usually been light/heat stress. It could be related to a deficiency, but if you're finding that the tips are yellow closer to the heat / light sources and the problem doesn't exist lower down on the plant, then id stick with it being heat stress.