Sick-looking Yo-Yo Loaches

[jesse99]

Hi everyone,
I’m Jesse, and I’ve been keeping a small group of Yo-Yo Loaches (Botia almorhae) in my 55-gallon community tank for about a year now. Recently, a couple of them have started showing some concerning signs. I’ve noticed red patches on their underside near the gills and slight fraying on the fins, along with unusual lethargy and hiding much more than usual. A few even seem to be scraping themselves against the substrate, which makes me think it might be some sort of parasite or bacterial infection.
Water parameters are fairly stable (ammonia and nitrite at 0, nitrate under 20 ppm) Pips NYT, so I don’t think it’s just a water quality issue. I haven’t added any new fish in months, so I’m a bit stumped.
Has anyone seen this with Yo-Yo Loaches before? Would you recommend starting with a salt treatment, or is this more likely to need an antibacterial/antiparasitic med? I’d really appreciate advice from the more experienced loach keepers here before I risk treating incorrectly.
Thanks in advance,
Jesse