I really need to write up a quarantine protocol for hobbyists, something along the lines that public aquaria already follow. Normally I agree with not treating animals except for hyposalinity and chloroquine right off the bat; however, being that clownfish are very succeptible to such diseases as brook, amly, and crypt I see nothing wrong with preventative measures. A recent case experienced were lionfish and spadefish testing positive (necropsy) for amly and dieing within 24hrs. with absolutely no tell-tale signs of disease or other malady and previously treated with chloroquine. Go figure. I guess my point is, quarantine tanks are for treatments and those who wait to treat allow disease/infections to set-foot and often leaving the aquarist running to catch up before it's too late. There are exceptions to every rule, but sometimes animals come in with a higher % for specific problems and they must be acted upon.
As far as your clowns, I would only treat with Formalin minus the Malachite and do not mix Meth. Meth and most, if not all, medications will disrupt nitrifying bacteria and if not monitored could very well lead to NH3
issues and possibly a drop in oxygen.