My 20 gallon can definitely handle another fish. I have 2 clowns and a royal gramma. I love wrasses swimming styles however there are alot of opinions on tank size. With sand my tank is 19 by 14 by 14. I have heard people keeping sixlines and fairy wrasses in 20 gallons and even in a fluval evo 13.5 a yellow or silver belly wrasse. Ive only seen in my lfs pink streak, fairy, sixline and halichoeres. So what are your opinions on any of these for my tank? I think from reading that fairy and sixlines are out but I would like to hear your advice before I buy one.