[Randy Holmes-Farley]

I've not seen much info or commentary from the many posters here with elevated phosphate (or nitrate) that connects phosphate and bleaching. It leads to browning due to excess zoox, and to algae problems and slow hard coral growth.

Low alkalinity will certainly stress hard corals, and I would not recommend keeping it belie about 7 dKH. That said, most folks do not typically report bleaching, but rather other undesirable effects, including corals dying.

Do you know it is bleaching (expulsion of zoox) and not something different like RTN? Have any of the corals reacquired their zoox?

The effects of elevated nitrate on corals is fairly mild and not well documented, IMO.