Vicky,
It depends......
Many people keep way too many fish in their ponds, either because they like the way they look, or because over
time the little buggers become big buggers and also they reproduce. While there are many "Rules of Thumb" for
how many fish for a particular pond, I prefer one that allows the fish to survive in the event of a power failure that
may last a couple of days. For this reason, the number of gallons and bio filter size are irrelavant as compared with water surface area, which is how oxygen gets into water naturally.
Other than water surface area, the important factor is how many pounds of fish you have. This is a measure of
how much dissolved oxygen is needed to keep the fish alive without artificial aeration, such as a waterfall. The best estimator of fish weight is length. My calculator is designed for koi, so short stubby goldfish would be slightly different, but not significantly.
How to use the calculator:
First, print the page. Then take it out to your pool and count your fish. Count the number of fish that you have for
each size, placing a mark beside appropriate cell for each fish. Then count the number of each size of fish and
enter that number in the appropriate cell. Return to your computer and enter your data. Don't forget to enter "0" in
all the cells where you have no entry, or your answer will be "NaN".
Enter the average length and width of the pond and click on "calculate". You will see the pounds of fish in your
pond and three different answers as to the pounds your pond might support: Maximum, Recommended, and Safe.
Safe is for a pond with no areation or biofilter.
Your pond has an effective surface area (assuming no water lilies) of 64 square feet. If all your fish were 6 inches in length, you could have 90 of them but if they were 15" fish, you could only have 7 fish.
See the calculator at :
http://www.gardenendeavors.com/rack/web17.html