Goldfish care fact sheet Goldfish make great pets and with regular feeding and tank maintenance they can live for over 10 years. Under good conditions in a large tank some varieties can grow to 30 cm.  Environment -          Goldfish are coldwater fish and do best at 18 to 23° Celsius and a pH of about 7.2 (water that is very slightly alkaline). -          Fish tanks are preferable to goldfish bowls as they have a larger surface area for gas exchange and allow more room