I am not an expert by no means, but a little brain storming. I am currently trying to save a GSP colony and I don't know why it is melting. One common factor you and I both have is the coral was in close proximity to a hydroflo. I know some corals like a strong flow, but could the constant on and off spurts of water over the coral be causing them stress?
Once again, I am not an expert but I wanted to throw that idea out there and see some more experienced reefers responces.
Good luck,
Chris