just about the only clown you could do would be a false perc, a pair would be pushing it, but, you could do it as long as you stayed on top of your water changes religiously, a false perc is also known as a ocellaris clown, they're some of the smallest clowns readily available to us as hobbyists, averaging no more than 3" long in most cases, so, one could do it, 2 could be done with religious water changes, and, IMO, the b&w ocellaris clowns are the better lookin of the clowns LOL