i never use salt if ive had an ich outbreak so i cant comment on that but i can give you a loach safe alternative. when i had loaches i used interpets anti-whitespot med. works great and you dont have to cut the dose as with other brands such as waterlife.
i have heard of a more resistant strain of ich going around, how true it is i dont know. it could all be rumours and fishkeepers myth but if you look at our ailments it makes sense that after decades of the same treatment a resistant strain would emerge. it reportadly had an increased resistance to salt and meds needed an extra week or two of treatment.
ive dealt with a difficult case of ich, it took three weeks with waterlife's protazon med at full strength. i dont know if it was more resistant or if i was just having some bad luck.