I made a change to my tank a few weeks back that I thought was note worthy. I was having trouble keeping some colors on some of my acros (not all) as well as had trouble with some discosoma and rhodactis shrinking and zoas fading away. I had suspected it may be related to bio pellets and have had that suspicion for a while especially when it came to certain mushrooms and zoas.
Well, I let my bio pellets totally deplete and did not refill them. Within a week, I saw some colors coming back, especially greens and yellows and some purples in acros. It has now been over a month and the acros are really looking good.
I guess the bio pellets out competed some of the corals for something, nitrates and phosphates were still measurable when I ran the bio pellets. My plan is to continue without bio pellets for now and see what happens.