Bullfrog skin problem...

[gspcom]

Hello all - I have kept an adult male bullfrog for a few years now and he has always had a lighter patch of pale, smooth skin on the top of his back. It was like this when I got him and didn’t seem to cause him any problems but recently the skin seems to be getting lighter, looks thinner and you can sometimes see red veins under the skin. This area on his back is always left attached when he moults so every time this happens, I have to place him in his water dish to soften the area so the skin comes free.

As for his set-up, he as a 3ft glass exo terra with mesh lid and a heat mat placed against the side of one end. He has a deep water dish and damp coconut fiber substrate deep enough to bury himself if needed. No additional lighting is provided, just indirect light from a nearby window. There is a night time temp drop also.

Any ideas on how get his skin back to a healthy condition? Picture attached also...