Favia tissue turning to mush

[DriftN201]

I recently received a new favia coral from a reputable online vender but I left for a few days this weekend. When I came home, my favia looked like the flesh was melting away. I took it out of the tank and tried to remove any heads that were rapidly dying. When I came home from work today, all but 2 heads are completely dead. No other corals look affected. The frag was on the bottom of the tank but I do not know the par. Zoas next to the frag are doing fine. I also have some hermit crabs and bristle worms in the tank. Nitrates are up to 40-50 ppm but I think that is mostly from the dying coral. It was close to 20 on Friday. Alk had a bit of dip while I was away from 9 to about 7.5. My main concern is that this might be an infection or bacteria issue. I have removed the coral and I am soaking it in amino acid but I think it will be a total loss. Any help would be greatly appreciated.

 

[DriftN201]

Do you guys think this might be a bacterial issue? Too much light? Hermit crabs?