i dont know how the fish in other parts of the world are but all fish in Australia that are imported have to have a mandatory qt from what i remember with either the supplier of store.Everyone had the ability to quarantine. All it takes is a 10g tank and a HOB filter. Your other option is to buy qt fish. Sounds like you are going to learn the hard way like 99% of us do.
if the fish is eating nori and grazing algae and there is no signs of flukes or parasites there is no need for extra measures. just feed the tank and see how he goes for another week or so.I wish I could qt, it just isn’t possible right now. I can try to do a hydrogen peroxide dip. (If that’s what h2o2 is).
(edit) wrote this reply before the other message loaded.
I can maybe have a 5-10 gallon to have as a qt/observation. I do try to do my best with keeping healthy fish but I know a qt is the best way. Eventually I’ll be able to have one.