Question
We have a 500 gallon pond with a waterfall for aeration. We also have 18 goldfish. Last year they had 120 babies which we culled (gave away). How many goldfish can 500 gallons support?

Answer
Hello Richard!
There are rules of thumb and general guidelines out there, but they really do not tell the entire story, nor do they always work.
The real story is that each pond is different and how many fish it can support depends on many things: how many plants there are, how good a pond filter it has, how religious the pond owner is with putting beneficial bacteria in the pond,the quality of the pond fish food used (quality food does not generate as much waste), the surface area of the pond,the size of the fish, etc...
The best I can tell you is to measure your nitrite and ammonia levels on a regular basis and watch for signs of problems with fish health (dropsy, sore spots, flashing, gasping for air).
One thing to take into consideration is the need for oxygen the fish have. Although the waterfall may provide enough oxygen for quite a few fish, if the electricity fails it could become a problem very quickly.
I would probably not go much over the 18 fish you have.
Brigitte
www.pondmarket.com