I'd suggest a look at liveaquaria.com at the nano tank suggestions they give to find a good specemin. Also depending on the exact type of clowns and goby a ten gallon could work. I have a pair of black percs and a (I forget the exact name right now) goby in my 12gal nano cube. Which is really only about 10 gals. If you try and break the rules though you have to be ready if it doesn't work out. If the fish in my nano start to get aggressive or if they just get to large, I have a 55 and a 120 to rehouse them in.