I have also had this happen, I started aggressively adding Nitrate to try and maintain levels over 5PPM and I got tip STN all over the tank, thriving colonies loosing tissue from the tip down. I stopped adding it and things seemed to get better, then I would occasionally add by hand and things seemed to do fine,.. then I would put it on a doser and everything went right down hill again.
There is a small part of me that makes me think that somehow the tank didn't like Acropower and NO3 dosed together. I have no basis for that belief other than one or the other seemed fine, but together I had problems. Although, to be fair, I never dosed them alone as aggressively as I did together.
I still don't like the idea of 0, and I think the corals do better with some NO3, both in color and growth. Since I had the issues I took Acropower offline entirely, and I test then dose to about 3PPM NO3 once a week, then leave it alone for the entire week. Usually by the time I test again I'm below 1, sometimes I'm back to 0.
Whiskey