A couple things that jump out to me, phosphates and mag inhibit coral growth. Proper level mag doesn't cause any problems but really high mag will.
When my mag is out of whack ( balance with alk and cal) for an extended time and my phosphates are low, my corals will stn at the base. I discovered this when I had a bad mag test kit. I noticed my sps had good color except purples were brown. Try comparing your mag test to another one. Low mag will cause a similar problem...it has to be balanced. There is a large window to have mag levels, but it is important to stay in the window.
I've also seen stn from the base with high phosphates, your phosphates are measuring fairly low...how did you measure them by the way?
I think I read you're using dry rock?.?. I haven't seen it personally (I don't have dry rock) but have read about this, dry rock is notorious for leaching phosphates. If the acro is attached to a rock that is heavily leaching phosphates, the leaching phosphates can inhibit coral growth and cause stn. Because the coral is so close to the source. You could test if this is the problem by taking the effected corals off the rocks and attach them to plugs and put them in frag racks or another rock. Is the effected corals start to stn where they touched rock? Again, this is something I read about...not first hand experience.
If you had any major swings in any of the big three parameters in the last six months, that could be your problem as well. A lot of times the effects of a large swing are not seen till several months later after the reefer has forgotten about it and thinks they are in the clear.
When my mag is out of whack ( balance with alk and cal) for an extended time and my phosphates are low, my corals will stn at the base. I discovered this when I had a bad mag test kit. I noticed my sps had good color except purples were brown. Try comparing your mag test to another one. Low mag will cause a similar problem...it has to be balanced. There is a large window to have mag levels, but it is important to stay in the window.
I've also seen stn from the base with high phosphates, your phosphates are measuring fairly low...how did you measure them by the way?
I think I read you're using dry rock?.?. I haven't seen it personally (I don't have dry rock) but have read about this, dry rock is notorious for leaching phosphates. If the acro is attached to a rock that is heavily leaching phosphates, the leaching phosphates can inhibit coral growth and cause stn. Because the coral is so close to the source. You could test if this is the problem by taking the effected corals off the rocks and attach them to plugs and put them in frag racks or another rock. Is the effected corals start to stn where they touched rock? Again, this is something I read about...not first hand experience.
If you had any major swings in any of the big three parameters in the last six months, that could be your problem as well. A lot of times the effects of a large swing are not seen till several months later after the reefer has forgotten about it and thinks they are in the clear.
