I know this is an old post, but I am having a similar problem. I have a trachy that was big and fleshy for almost a year under an ATI Hybrid T5/LED fixture.
I then added in some fish (kole tang, coral beauty, pair of wrasse, couple clowns) from another tank that was being broken down. To compensate for the increased bioload I then started dosing NOPOx.
Shortly after the fish addition the trachy bleached. Nothing was picking on it. SPS are fine, euphylia are fine, zoas are mostly fine, goniopora are fine, duncan coral is fine
I moved the trachy to my coral QT tank (Radion Xr15 pro) and now it seems to have recolored and puffed back up in like two weeks. I'd like to move it back to the display tank.
Wondering if anyone has any thoughts? Can it be the lights due to increase in clarity from the NOPOx? I moved it to a shady spot it seemed to do nothing, but I can find an even shadier spot. Par on the bottom is 200 to 250 ish.
I also have flatworms though they don't seem to bother anything, I've had them since set up and dip my corals.