How do you keep goldfish healthy in a bowl?

Goldfish need more space than what people may believe; one goldfish needs a 20 gallon tank, and you need an additional 10 gallons per fish after (so 2 goldfish in 30 gallons)

This is not just about their potential size (which is big), but the amount of waste they produce. The old adage of inches of fish per gallon is completely incorrect when it comes to goldfish due to being high waste producers.