Retroactive Quarantine?

I've recently setup a new 55 gallon tank. I let it run for a while,
then stocked it with a bunch of plants and three tetras from my LFS.

Yesterday, I read on the skepticalaquarist.com a strong argument for
quaratine for new fish, and for salt and parasite treatments, and for
treating plants as well. It sounds like a really good idea.

My question is, if I were to quantine my fish now, in a small tank that
I could treat and change lots of water on, would my main tank be
sterile in a month, having been free of fish (but not snails)? If
things would live on in the main tank anyway, what would be a good
course of action?

Thank you muchly.