You also need a filter. An air pump does not clean the water, it just stirs it around a little. You definetly need a bigger tank. And remember to feed only what your fish will eat in about 2 minutes, once a day, especially in a new tank. If there is any food left after 2 minutes, you must remove it. Or it will rot, and further degrade your water quality. And the fish won't eat it anyway.