Stocking help 20 gal cube

[greyhunter]

Hi everyone currently i have a waterbox 20 with a pair of small timid clowns and a firefish. I was wondering if i could add 1 more fish to the tank or would it become to crowded then? If i could add one more fish do you guys have any suggestions?

 

[ptrusk]

Neon blue goby. Stays small, think 2" fully grown and a nice splash of color. Mine bothers no one and my a hole clowns don't bother him. Downside, I don't think they are very long lived.