From finrot to white stringy goop?

[lemonpebbles]

I've been treating my betta Uno for finrot the past five days in a QT cup with AQ salt floating in his tank. He was starting to look really good until one morning (at around the second or third day) I woke up to find a lump of poo in his tank and the edges of his fins bloody again... Today I was about to start with tannins and AQ salt wen I noticed some clearish white goopy stringy stuff floating about the cup and one was hanging onto his fins.... His behavior hasn't changed any though, he's eating and greeting me just as usual. What is this stuff and what should I do about it?