Hello, reefs.com, this is my first post! I saw the topic and thought I could weigh in since I had something similar happen to me recently.
Have you considered that your soft corals may have started emitting toxins into the water that is irritating your corals? This is a self defence mechanism that most (or all??) soft corals have, I believe. I too have kenya trees and some other softies mixed in with my LPS, but I don't have any SPS. One day I noticed that all of my corals were suddenly irritated by something, and most of them were all sucked in completely for a few days. After testing and retesting I found nothing wrong, so I decided to move my kenya trees and toadstools to another tank, since I read that these can be the most likely to emit toxins. I also replaced my carbon and did a big (30%) water change. I did another water change 2 days later. After about another day my corals perked up and things were be back to normal. I too noticed that my LPS (trumpet corals and frogspawn) were the least affected by whatever was in my water. This still doesn't prove that it was my soft corals emitting toxins, it could have been a total coincidence, but its something you could look into. I had recently fragged my toad stools, and had moved some corals around, which could have triggered this defense mechanism, who knows.
Welcome to MR.
It's definitely something else to consider. But then the question would be why would it be releasing toxins. Irritated by something I would assume would lead to that. Which might lead me back to something wrong with the water. Thanks for the input though I'll definitely keep it in mind if iodine doesn't help.