There is a store in Coralville, which is right next to Iowa City, called "Coralville Bay" that has nice freshwater fish. Their plants are not usually very happy though. We also have a PetCo which is decent for a big box store.
I live in Coralville and I do most of my business with Coralville bay. I get my ro water there because I don't have the best luck with Coralville's water and plants. We also have a petland and there are a few stores in cedar rapids which is not too far away.
Hope you have fun in the area.