Can goldfish live in a small pond without some type of air filter? We run our pond filter
about ten hours a day. Is that enough to give the goldfish air? I also found out that
the temperature in the pond should be 60s if it gets too hot like 80 and 90s - the fish die.
I'm a noob, so take that in consideration in my answer.
Goldfish are hardy and tolerant of a wide range of conditions, particularly the common.
As far as oxygen, this varies depending on temperature, surface area and time of day.
Cold water holds more oxygen than warm. So a warm pond (in the sun) needs more attention.
If you have algae (common in a sunny pond) or a heavily planted pond then you have a day/night pond cycle. With the plants providing oxygen in the day and taking in oxygen at night. So the oxygen level in the pond falls throughout the night. If you are adding air, then it is most needed at night.
The filter won't add air, that is done in the spray. This is all about surface area. A pond with a large surface area per volume will have more oxygen diffusing in. Smaller spray droplets falling for a greater length of time will put in more air.
So, to get more O in the water, you either run a fountain or a waterfall, add air in the filter line by having an air tap next to a venturi (the lower pressure in the expansion sucks in air), or by pumping air to an air stone. Smaller micro bubbles are more efficient. You may wish to blow bubbles 24/7 or at least at night.
Myself, I'm trying for a more natural pond (or at least more artistic) rather than a perfect one, so I'll break a few rules.