Bacteria, algae, poor aeration, chemical imbalance and waste are several causes of cloudy water in a goldfish tank. Goldfish are messy and it doesn't take long for the water in an unfiltered bowl or tank to become cloudy.
To prevent water quality problems, keep goldfish in filtered and treated fish tanks rather than small bowls. If you must keep goldfish in a small bowl, change and treat the water daily. Goldfish can grow very large and can live in a variety of environments, including in tropical fish tanks. In a healthy and clean environment, goldfish can live for several decades.