I have a 6 gallon as well so I know that finding fish for a tank that small can be a challenge. As for a goby... A panda goby or clown goby would be fine. Wouldn't recommend a manderin goby as it would eat itself out of house and home quickly. I love our blenny we have in our 6 gallon. He's a tailspot blenny. They are cute as a damn button and have one heck of a personality to boot
