my fish needs company i think

[7808]

i have a pretty small tank, 20 gallons. i have a clown in there whos been in there about 3 weeks i i think. he seems like hes doing good. eats and all, only other thing in there is a crab. id like to get another fish, but im not sure what to get, id like to get another clown for him but im not sure my tank can handle to of them. i have 15lbs live rock and a hob aqua clear 10-30gal size with just a sponge, carbon bag, and some blue plastic net stuff in a mesh bag. also a micro algae ball the size of a softball.

any suggestions what other fish i could get?

id like to get something else that cleans also but id ont want to overload the tank