guppy diseases

Hey thanks for taking the time to read this and any advice is much appreciated. I have a 20 gallon tall. With hang on back filter for up to 30gal. Also installed a dual spongefilter to add for oxegen. It is heavily planted with hornwort, apotogen, dwarf water lily. I cut out a bunch of excessive...

They have these clear barely visible strands on their back tail fin. I don't notice them anywhere else on them. I don't notice anything differently about their fins, I don't see any white spots on them, they shimmy and swim vertically. The one female who had it had 1/3rd of her tail fin...