A six-line? I've never kept them personally, but I've seen a pacifist six line do fine in 29 gallons. Key word being pacifist. I think the problem with these guys lies in aggression. I've known several people both online and in real life who have lost fish and even clams to these fish.
Do you have a ballpark figure of what size tank were you looking to get, Ram?
Live Aquaria states they grow to 3 inches but I think in a small tank, anything less than 20 gallon long, there could easily be problems with aggression to other fish.