Goldfish Stocking Density
Goldfish are big fish, and as such, produce a great deal of waste. Goldfish are not suitable for small “starter kit” aquariums or fish bowls. They need adequate space for proper dilution of waste in order to thrive in a clean environment. When waste products build up in the aquarium, it leads to poor water quality. Poor water quality is the #1 reason that goldfish succumb to disease and/or death. You can avoid poor water quality, for starters, by ensuring that your goldfish are provided with adequate space.
So how many goldfish should you stock in your aquarium or pond? There are many opinions on this topic, but all experienced goldfish hobbyists agree that the more space you can provide your fish, the better.
At a minimum, provide 20 gallons for your first goldfish, and 10 gallons for each additional goldfish. For example, if you would like to have 4 goldfish, you can expect to need a 50 gallon aquarium or pond.
Stocking guidelines do vary depending on the size of your fish. A 1″ goldfish will not necessarily need the same amount of space as a 6″ goldfish. However, that rationale should not be used as an excuse to keep on overstocked tank. It is not advisable wait for your fish to grow larger until upgrading to a larger tank. If small fish are kept in a small tank for any length of time, there is some evidence to suggest that they can become stunted – meaning they will never grow to their full potential.