ASI may be right. Try adding some cal/mag and see if it helps. I think the only way to get nute burn in spots is if when u watered, a few drops hit the leaves.
One more thing. On my last grow, I tried using the bloom bulbs (yellow/red lighting) and I wasn't to impressed with it. When I use my grow bulbs from start to finish, the plants get bigger and therefor more weight...Personally I'll never use my bloom bulbs on auto's again.
I guess I should also tell you that I've been growing these auto's for 3 years now and veg. lighting all the way though harvest is the best lighting for auto's. My opinion. Like assholes and elbows, we all have them