Have you tried
Poly-Filter Pads? They will let you know what is in the water if anything, as well as remove it. Was there any glue or additive from plumbing allowed to seep in? Even more reason for carbon, just stick in sump either at drain lines or near return pump for a lot of flow. That'll help a lot as will what everyone else has said in doing some good water changes.
I think that the corals will recover, just start making sure the water is free of contaminants. Sometimes strange stuff gets into the water column, like copper, which can be filtered out quickly....