I would think that what is in there would be plenty of bioload without adding more. I have a 14g on my desk at work with a damsel, clown, watchman goby and a sixline. Any time I've tried to add one more fish, they always die. The ones in the tank have been there for at least a year or more since I first set it up. So I think mine is telling me it's happy the way it is.

If you try again and fail, I wouldn't give it another shot IMO.

Dee