If it was just nutes bottoming out, I’d suspect your colors would be affected first, paling. The TN could be anything to be honest.Ok..i see. N03 has been zero and p04 looking like .03. Looks like there's a lot of acro competing for nutrients with a refugium of sorts? Not sure if the n03 getting dosed is in an easily consumable form at that. May be easier to feed the system more food for fish. Either way..mariculture acros can come with a host of things to navigate for succeeding. Could be the low nutrients, could be too much competition for whatever trace elements are available, could be bacterial. The base of the one colony may be shaded out. I know it's not exactly a "that's it" reply because it could be a combo of many things. As mentioned earlier a fragging may be the best road to take on the ones suffering.
As suggested it wouldn’t hurt to dip a colony that’s affected to see if anything comes off. Have you done this? If not, why?
In my experience with mariculture colonies and wilds, they just don’t do too well after a few months and start to peel. I see most people have success with them when they mimic natural parameters and with good metal halides.
That could be a part of your problem too.
In reality, who knows?