A sixline would work, but just be aware that they're very likely to become a bully at that tank size, and they're absolute pitbulls when they bully punching WELL above their weight class. The flipside is they're insanely hardy and likely to absolutely decimate pest populations. Pink streak and possum likely would too but they're much more cryptic and significantly more challenging to keep/pricey.My lfs has red fairy, yellow cori wrasse, sixline atm