the logic would be 2 clownfish, doesnt matter if its designer or not as most dont have as many issues as they used to, but lets say 2 wild caught percula or skunk clownfish would make a great 20 gallon tank. Maybe one or 2 more small fish as that is what many people on this forum have and have had success with and havent been overloaded with nitrates, now thats logical. Doing something that only you believe would work and against at least 20+ people and respected websites telling you not to is illogical