Hmm... 9". At that size, I would put it into a 12qt tub. I had my new snow girl in a nice 10g tank for about a week before I saw her falling from the top all the time because she wanted to crawl around the lip just under the lid. Same thing with my Anery when she was in the tank. Now, I don't put corns into tanks until they're too big to get into that little space.