I used to live in Cleveland and I always went to RMS Aquaculture. It's near the airport. It's huge, and there was always a really diverse selection of freshwater and saltwater fish. Plus pond stuff, reptile stuff, some small mammal stuff. Lots of supplies as well. It was great - I really miss it, I'm in Cincinnati now.
There was also a really great salt water place I went to once with a friend, it was further out Southwest I think and I can't remember then name. If you're really interested I could try to ask for you. But otherwise RMS Aquaculture it is!
The address is on Engle Road, but the actual Suite number to RMS faces Sheldon. The parking lot is all connected, but you might be confused the first time you go there because the door isn't literally on Engle...