What is wrong with this guppy?

The male in the picture was, until the last week or two, acting normally (swimming around the tank, eating, that sort of thing). Almost overnight it began basically hanging out in one spot for nearly hours at a time, moving very little. It would mostly be in parts of the tank with minimal water circulation (eg near the intake or output hoses for the canister filter, but mostly behind them). When I fed the fish, it moved around a bit, but then would go back to basically hovering. The ONLY issue I noticed was the white patch on its side. I don't see any other fish acting similarly, and don't see similar patches anywhere else. The only issue of any note was that I had an african dwarf frog that died from dropsy in the last few days. I don't have any idea if they are related, but figured I'd mention it.

The water is fine. No ammonia or nitrite at all, and minimal (maybe 10 ppm) of nitrate. The pH in this area is a bit high, running near 7.6 or so. I do regular weekly water changes of 25% or so.

Any guesses?

I'm afraid but guppies just eventually fall to pieces, sometimes you get lucky and have a strong one. They have been so highly bred in aquariums that genetically most of them are unstable.