You might have put too much of fish food that made the water murky. Just try my trick : take a bowl of water and let it adjust itself to the same temperature as the water in the aquarium, then carefully transfer the fishes to the bowl (never take out the fish with your hands, use a laddle instead) throw away the murky water in the aquarium and clean it thoroughly and then pour water to an adequate level. This time also the water temperature should be just the same or the fish may die. When temperature level becomes the same put back the fish in the aquarium and then its all okay.