I think most people use 20H, though personally I like having a little more room and have 29s. Mostly personally choice and what will fit best in your fishroom. I started with all external filtration, moved to using both external and sponges, and today I've got nothing but sponges going. There are a few of use here on SD from Wisconsin, though it seems like the number has about doubled recently. Some really good people around, hope you enjoy SD, welcome.