a month.. you need to cycle the tank!!
http://www.directtropicals.co.uk/index.php?main_page=page&id=8&chapter=0&zenid=c3f0707634e01e52fbd6029e1cabce1e
three days is rubbish, you will kill the fish, a goldfish needs 10gallons each fish and the tank needs to be cycled with double filtration or your fish will die