That's true Michelle but the polyps will never reattach - or so they say, and its hard to keep them in place. A lot of these LPS produce a lot of slime when the polyps are touched so it would be hard to keep them stationery to give them that chance to form a skeleton, if that is possible at all. The skeletons on the other hand could regrow over a few months of time if there is even a single cell of tissue remaining. Even if you have pulled the skeletons out of the tank already & they are dry, you can place them back in & see how they go.
My experience with LPS so far has been that most of the things that affect them are usually ongoing & once it has been corrected, they then recover - which is why I'm leaning towards an ongoing problem rather than an event (although a massive change in temp hot or cold would definitely have after effects). Brown jelly is very obvious to the naked eye & takes fast effect so we can rule that out IMO - if this is a worry, doing a coral dip is an option, although I have found that in the two times I have spotted the beginnings of it in my tank, I have simply blasted the BJ off with a powerhead & it has stopped the progress completely & recovered.
Something like lighting being on for too long each day could take a few months to affect them to the point where they start to bail, which is why I was asking. Lighting also affects pH levels which @
holly 's post just reminded me of. If there is some sort of metal poisoning going on, a drop in pH increases the solubility of these metals. pH naturally drops at night when the lighting is off, which is why some like to keep a light on over the fuge to keep the levels steady.
Your parameters are spot on Ant, I'm pretty much at a loss as to how else to help you here and I think you know more than enough to spot the problem on your own - hopefully something someone has said in this thread will help.
My only other thoughts are: are you using anything on your arms & hands or spraying anything near the tank? Using anything topical? Do you use something in the shower on your skin that could be poisonous to the tank? I'm a little worried whatever is going on could affect your other inhabitants & this was the first warning sign. With polyp bail out there is no need to remove the skeletons from the tank as they won't affect anything. Maybe just to be sure hands out of the tank would be best for a few weeks.