Help: Firefish Flashing and Hiding Often

[ReeferWarrant]

I got a firefish from my buddy that was pretty banged up from his other firefish. I've had it in the tank for about 2 months and it was always pretty active and made it's home in a cave. It eats fine and it's fins were pretty badly damaged, but are now fully regrown. The problem now is I will see it randomly flashing in the sand and then just now I looked at it's belly and it looked to have a jagged piece sticking outward but now it has disappeared. It has been hiding a lot lately, I initially assumed it was just getting harassed by my bicolor blenny. Now that I see this protrusion, I'm second guessing myself. Curious if anyone has seen anything like this?

 

[Big G]

Darn Firefish get all kinds of wounds, torn fins, etc. diving into the rocks/caves to hide out. Amazing the damage they do to themselves and then usually recover. Keep an eye on the that spot for a white/white-ish filmy area, redness, or necrosis.