The blackout thing is a goofy idea brought about by the idea that the parasite might use sunlight to "see" which way is up, and if in the dark it will just sit on the bottom & starve.
This is ridiculous. Even if it did work, the fish would likewise sit on the bottom in easy reach if the ickies.
Other forms of ick which aren't really ick but collectively lumped with it might indeed actually need some light to hunt, but again it won't really work.
Formalin is good. Avoid copper & malachite with clown loaches.
Salt baths are temporary treatments involving placing the fish in salty water for a short time, as the name suggests, but they aren't any good against ick, really. They do help nail the ickies exposed to the water on the gills, but the ones buried under & protected by the fish's slime are unaffected. Salt baths are good for things like infections, but not really worth the trouble for ick.
Putting salt in the main tank & raising the temp to 86 or so will work remarkably well in most cases, although catfishes aren't very tolerant of it.