Fishdom 3: Special Edition

Every few levels you'll unlock the ability to purchase a new aquarium. Once you reach level 37, you'll unlock the ability to purchase as many aquariums over 8 as you want. They have a steep increase in price and are the most expensive thing to buy, so you'll need to save up money to buy them. I highly recommend buying a new one as soon as one unlocks because they give you a lot of XP, so it's better to use that towards reaching level 48 rather than buying them later when you don't need the XP.