Thank You!!!!
Sorry, But yes, exodons would be great! The only sticky spot is keeping them, "healthily overcrowded".
By this I don't mean 'stuff as many of them in a tiny tank as possible', as this is never healthy for any fish. what I mean is; keep enough of them so that they all share an equal beating. If you put two or three exodons in a 20 gal, one will get picked on and likely be killed. The group will then move on to the second-wimpiest fish in the tank and beat up that one. this process will continue untill there is only one fish in the tank.
However, if you keep enough of them that one fish can't get singled out.
In short; five or average-sized exodons should do well in a 20 gal. Just keep them well fed, well filtered, and provide plenty of visual barriers. these fish are small, pretty, VICIOUS, and have plenty of attitude.