Recently, I've been finding dead Sewellia loaches in my tanks. They had patches on them. I started to treat with antibiotics (Maracin 1 and 2), but no improvement: they were still dropping like flies. One day looking good, next day dead with patches.
Then I realized that the loaches were dying, and only subsequent bacterial degradation made them look patchy. I suspected parazites and proceeded with Praziquantel (sold as PraziPro) treatment at twice the dosage (this was not the time to go easy). The reason to think parazites was that I also saw some of them pooping their intestinal epithelia . . . it looks like empty sausage casings.
Overall I lost 6 of 12 loaches at a rate of 1 or 2 a day . . . if there is any consolation prize, it is that the 6 that are gone were males and I now have an even ratio. During the last 3 days (since I started anti-parazite treatment), I have not had any death. Fingers crossed that this was it
Cheers,
wm_crash, the friendly hooligan
Am going to edit the first post too.