Ahhh. Maybe that's the problem. ;)

Potassium permanganate is used more now-a-days to clean up plants. However the old fashioned soak of plants in a gallon of water with a dissolved teaspoon of alum for 20 minutes may still be more effective.

The alum must be dissolved in a small quantity of hot water before being added to the gallon jar or other soaking container. And as you suggest for other treatments, the plants must be rinsed well and then rinsed again. That should be good for getting rid of leaches and transient fish eggs, most snails and many (probably not all) disease organisms.

Your salt treatments are among the safest because trace quantities of sodium chloride are not likely to be a problem in a tank.

I knew a guy who used to drop pond snails in an alum mixture just to watch them shrivel up. He may have been a little troubled...

Those darn Malaysian livebearing snails would probably just close those nearly indestructable trap doors and going about business after rinsings. :(

By the way, would putting plants in pots let the loaches forage without bothering the plants too much?

Would large loaches inhale baby guppies by the bye? (That mouth size factor again.)