I was at work today and a person brought in a fish just to give us. So we accecpted it and I took over from there. I put him (with him still in the bag) in the tank where I would put him. I took out some water from the bag and put in some water from the tank. I did this for 5 or 10 minutes and I noticed the fish started to loose his top layer of skin. Only on his head though would his skin come off in layers and then I noticed his gills got really red. And this has never happened to me so I got a bucket, filled it with water from our tanks and put him in there. He then turned a pale color and u see his veins, this was freaking me out. 5 minutes later, I put him in our tanks, his color returned and his skin stopped shedding, his gills went back to normal. WHAT HAPPENED?