Dear sir, instead of having a variety of fishes who shares different habitats, one should lay more emphasis on the ecosystem of the aquarium. Your fish tank is relatively small and therefore just 4-5 goldfishes including one black moor (from feng-shui point of view)without including koi or angels. Change water after at least 3-4 weeks time (use good filters and O2 pump) and feed less pallets to fishes. Add prescribed amount of anti-fungals and please add little bit of salt at the time of changing water/cleaning the tank.