Im typically a minimalist with medications so no i never tried anything else besides salt and heat. The red circle loach is clearly visible between 30-40sec of the most recent video i posted on last page yesterday. You think it is worth separating and treating this loach with another method? Ive been monitoring him and like i said he starts to look better when i keep the very small pellets in the mix so ive just been hopeful with that, giving it time.The PraziPro treatment doesn't seem to have resolved the issue. Did you try anything else? Prazi is really only an effective treatment for certain flatworms, and ectoparasites, and is not always going to have any noticeable effect on internal pathogens, such as spironucleus aka hexamita, etc. You might find this paper interesting. Praziquantel use in aquaculture – Current status and emerging issues - ScienceDirect
Personally, I would also try feeding them epsom soaked foods for several days and see if the fish in the red circle comes around. One of the 4 oddball loaches that I currently own (6-7 yrs old now) initially came to me as a runt, and on the skinny side. The previous owner thought that he was sickly. I fed the entire group NLS Hex Shield (basically a garlic/epsom salt infused pellet) for several days, then again a week later for several days, and he seemed to make a noticeable improvement shortly after. He's still the smallest loach in the tank, but filled out, and I believe that he is also the only male, so being smaller than the rest makes sense. Good luck.
The prazipro definitely had a marked effect on all the fish circled. But like you said may not have finished the job. I dont find hexshield available at my LFS but it may be worth me searching out.