Okay I have a 500 gallon pond with about 15-20 goldfish in it (commons and comets) and I really would like to take away the fountain that is disrupting the surface of the water, making it hard to see the fish and not giving the plants enough sunlight. The fountain is an extension from the filter that just pumps the clean water out in a spraying fountain straight above the water, creating lots of ripples, bubbles, etc. So my question is, if I stop the fountain frim spraying up, will there be enough oxygen in the water to keep the fish comfortable? If not about how many submerged plants would I need? I already have about one bunch of anacharis plants in there, some duckweed floating about, and some lily and aponogenton bulbs down there that I don't think are getting enough sunlight to grow currently. I have looked all over but haven't found an answer to my question.

(The answer is probably really simple and right infront of my nose, but please if you can help me, help me )

Probably not unless you live in a cooler area.

If the oxygen level is enough without the fountain depends on the filter. Without the fountain extension, how does the water enter the pond after it gets filtered? Is it one of those submerged filters?
If yes, then you need something else for oxygenation. You can try an airpump with an a few airstones, or a filter that is outside the pond, and when the water splashes back into the pond from the filteroutlet, then oxygen will enter the water while it touches the air, and runs into the pond. Or a simple powerhead will do as well. Having it under water, very close to the surface of the water, and pointing it towards the edge of the pond. That way you will disturb the water surface, where the most oxygenation takes place. Anyting that disturbs the surface is ideal for it. The fountain did the trick, but there are the above mentioned methods as well that don't disturb the plant life all that much....