My fish died within 8 hours of showing signs. Often quicker. With no outward signs other than out of personality behavior.
My tanks were planted, No nitrate readings and complete cycle, even now.
There are no children here, and no one that messes with my tanks. I have put the fear of god into the people I live with for just touching the glass, So they know better.
And mine was nothing like yours as far as slim coat and swollen gills and dark patches. The there was only one out of 4 that showed any swimbladder problem.
Every fish died from a different reason, One died of some thread-like fungus, the other had no fungus, but had something wrong with her swim bladder, the third died for unknown reasons. It wasn't a fungus but she had some peeling around her lps
. and the male that died last had no connection what so ever to the other tanks. Seriosly, No drippage, No using the samw tools, no moving plants.. Nothing.
Out of the 5 betta's I had, I only have one left.. and its my Original Female, that lives in the 29gal hodgepodge tank.