I would not use a 2.5gal tank for quarantine purposes - I use a 5gal for that purpose and I feel limited - not only in how many fish I can put in there comfortably but how much room the new fish have to move around - new fish need space to hide when they 1st arrive (I put a fake flower in mine and keep it bare bottomed) as well as to explore when they finally feel more comfortable.

From what I've learned here, a 2.5gal is good only for small shrimp & snails.