sounds like you have a very nice pet store... i wish i was so lucky.

as for it being a fish tank, it really doesn't matter as long as you give it a very good cleaning, which i am sure you were already planning on doing. a 5% bleach solution will work, just keep the bleach on the surfaces for about 20 mins and then make sure you give it plenty of time to dry out. if you smell any bleach, more washing with water and drying is needed.

the only thing i have noticed with switching fish tanks between different kinds of animals is if you use it for rodents, then try and put fish in it... you are going to have a very wet floor