You can make your own jellyfish tank fairly easily with supplies from craigslist. I'm going to be posting a youtube on it shortly at www.jellyfishart.com. You're correct that waterflow is crucial and you don't want any air bubbles to get trapped under the jellyfish, but there are a few different tank designs. You can go with a vertical cylinder or a regular square tank with rounded corners called a pseudokreisel. I have a lot of experience with jellyfish so feel free to direct any questions my way.