Fish can live for a long time with a chronic skin flukes infestation. In some cases, it isn't fatal at all. Remember, the parasites don't really want to kill their hosts since they would die as well. It's just that in small aquariums, the parasite load is much greater than in the wild.
I watched the video a couple of times and didn't really see much fin flicking or twitching. Still, those signs can be very subtle.
One option would be to treat the tank with Prazipro 2x, nine days apart with really good aeration. That is well tolerated by fish and most invertebrates. If the symptoms clear up, then it was flukes.
the trouble with FW dips as a diagnostic tool is that only one type of fluke is large enough to see in the dip water without a microscope (Neobenedenia) ....other fluke species would go unnoticed.
Jay