Thanks everyone. All my bettas are showing fin loss; I have the girls in the 29 gallon & my 1 male left alone in a 10 gal.
I don't know how to disinfect a tank, and I really can't consider it b/c the 29 gal contains live (=expensive) plants; 4 juvenile ocellifer cats & 13 TEENY oto cats, plus snails (that don't seem to live very long in that tank). These cats are showing no illness, but they, by default, are getting the KanaPlex.
I can add the Jungle Fungus Clear, too.
From what I've read, once bettas have a disease, you can't get rid of it, just treat the symptoms. (Info from Matt's Bettas.)
The girls look horrible, but all are eating and terrorizing the ocellifer cats! They (particularly Mist) waits for the cats to come out of hiding & has a face-off with them (the cats scurry away). When I feed the cats, she (7 the others) has to sample their food, which is not good.
4 bettas: Butch, 3-year-old violet male PK EE & 3 girls in a 30 gal sorority. I do not name the girls anymore! 1/2 of them die within a month.
30 gal: 9 Oto cats, 4 Ocellifer cats. Inverts: Cherry shrimp & 2 assasin snails.
10 gal.: Butch, his 5 oto cats, 3 assasin snails, and a few snails the assassins haven't caught.