What is your go to treatments for when you get new fish?

Is this what you mean for QT tanks? I saw Aquarium Co-Op say he does a anti-parasite medicine and then doses with Ich-X. So probably going to do that from now on

You first of all should have them quarantined no matter what for at least 2 to 4 weeks even if they are not showing any signs of diseases or infection.

You can decide to medicate them when they are in quarantine.

We've never bought anything specific to add to the tank when introducing new fish. We just kept them in their bags for a bit floating in the water so the temps even out. I don't think that we were ever worried about disease since we always bought from reputable shops.