You can easily keep a clown INHUMANELY in a 5.5G. Don't do it PLEASE. If you do a 5.5G, please, either keep it coral or invertebrate or nothing bigger than a neon goby or yellow goby. It's simply being a conscientious aquarist...and..minimizing contamination in a 5.5G. I"m sorry, but, I don't think it's fair to the clown.. Because others do it..or because others do it 'successfully'...doesn't mean it's right. SH