They are severum and p bass. Seems like their slime coat are coming off (like long thin strands) they're covered in ich. It like jelly-ish consistency surrounding its bodyI would not add salt, PToney; clown loaches are pretty high stress to it, and I think knives are too. Add some extra air stones or a powerhead aimed at the surface, cease or slow down feeding a good deal, and keep up the water changes.
ilike, what do you mean? On what kind of fish? Some fish 'slough' their skin, like hoplos, I think, when they have an irritant in the water.