About a week ago, my African Clawed Frog became lethargic, always staying at the top of the tank, not eating. I've had him for 6 years, and he's never acted like this. I thought he was just going through something, but it went on for about 3 days, so I looked up about it. It seemed like it was a PH problem, so I got the water tested, and the PH was high. I swapped him into his old tank that he did well in, and he started acting normal again, eating and all.

I got the PH down in my other tank the other day and put him back in. He was acting much better than he was, but this morning, 2 days after putting him back into the tank, I found him dead. He was acting fine last night, I don't get it and am devastated. It looks like he had flesh from his front right arm peeled off or something, which makes me think it might've been Red Leg, but I never saw a lot of red on his leg or anywhere else... I actually found some skin or something floating in his tank a few months ago, but only found this 2 or 3 times, and he acted normal so I didn't really think anything of it. Also, the tanks temperature was always around 73 degrees.

Here's a link to imgur, I uploaded a few pics of him. Maybe you can see what was wrong?

http://imgur.com/a/B95iY