I've lost my frog...

[Thehungrydozer]

... And I can't figure out why. I would assume my PH levels got off balance, but it's so hard to tell.

Robert was fine and dandy yesterday, he ate his food, swam around actively, and seemed pretty content. This evening I pop in and notice he's aying front and center in the tan, on his back, dead.

He's got a sore on his side that's red, and I'm not sure of he bumped something bad. He's not emaciated, and I've been doing water changes regularly. (For about a month 25%-30%) and for the past week haven't had a chance to test the PH of it, I ran out of strips and since I've been busy with midterms and the petstore is out of the way from college and work I haven't picked any up.

I can look at his hand and it looks like there is a little bit of a white fungus on him, I'm not sure if that happened before or after death. I also notice tank water has been evaporating rapidly within the past two days so I don't know if that upset his levels or not?

Any help for a distraught froggy owner?

[Thehungrydozer]

Edit: (Because for some reason I'm to ditzy to figure it out): 25-30% weekly I meant to say.