I think people might be missing the point here, you have four of the most aggressive fish in a tank that is the minimum size to accomodate one of them for life. Those fish will out grow that space quickly and if your seeing fireworks in there already it wont be long before that playful fighting becomes one dominate fish killing the rest. I hope you are planning a massive tank upgrade or on picking your favorite fish out of the four soon, otherwise get ready to waking up and finding dead tankmates. Placing fish in a small space so they fight is not cool and im surprised more people havent already burned you for it. I hope im wrong and this post was just a bit of fun and your already planning your next move for the welfare of your fish. good luck in whatever you do