You’ll need a 40-gallon tank for most loaches because they can grow to 12 inches in length. Many people mistake some loaches for eels. The yoyo loach’s appearance is more like a standard fish.

A 20-gallon tank is suitable for a single goldfish ... Many experts advise another 10 gallons per extra fish. In sum, you’re looking at about 40 to 50 gallons for a pair of goldfish.