My husband has a 10 gallon tank from years ago. His sister uses it as a holding tank when she cleans her bigger tank, so I am pretty sure it is still water tight. I have 3 children who would love a fish tank. I really like goldfish with their pretty tails, and my children loved these tiny neon fish the last time we were in the pet store. Could I mix those 2 fish (I know both are fresh water)? How many fish of what size could I put in this tank? Or, so you think I should spend the money and get a bigger tank? What size? I don't have a huge area to put it, but I want to make it worth my while.