Help figuring out cause of death?

[beaniesnbowties]

Tonight, my little golden albino passed away. he was a baby, about 2 inches in length. today he started floating. it began as just his rear/tail. i went on to work then came back hours later. he was floating at the top of the tank, slightly tilted sideways. i was instructed by the breeder to allow him time in a tub of cold water(treated with conditioner) but not to fridge just yet. hours later, he had passed away. i do not know why. the tank parameters were fine (ammonia 0, ph 7.2). his feet were red. his stomach was also red and bloated. he rarely ate(ive had him for a few weeks, kept im a fully established tank 10G tank). im adding pictures. can anyone help explain what migjt have caused his death? the look of his underside worries me a lot and i know it shouldn't appear like that.

 

[charleybambino]

Sorry for your loss. My guess is septacemia...massive bacterial infection

 

[auntiejude]

I'm sorry.
From the looks of the redness I'd say bacterial infection which progressed to septacaemia.