No my tank is 10 gal. But with two fish and two snails I really shouldn't add another "big" animal until either one of my snails dies or Fish (my old boy) passes.. which I have a feeling will be sometime this year. The ghost shrimp I'm told have almost no effect on the Bio-load so I should be able to have them. But like I said I need to do more research.
IMO you should always quarantine every animal you add to a tank for at least 2-3days. Make sure it is eating and pooping normally and it has a good activity level.