Lots of questions, but good ones, Keith. Here are the answers:
The stream flows into the pond, but only from about 8" above the water, not much of a splash. The fish usually only hang out around it when I am pulling things in the stream, messing up the water, they swim over to see if any goodies come down. Otherwise, they don't hang out there. How much water is moving? Not much. I have the skimmer in the middle of a curved inside edge of the pond. Stream is on one end (fed by the skimmer) and bog outlet is on the other end.
My pond is 17' x 7' ... so that would be 119 sq ft, not positive on the square inches, multiply that by 12? It is covered by lilies on about half of the surface area. I have about 20 fish now, had about 30. Largest are 6-7", most are in the 4-5" range, maybe 1/4 of them 3-4" range. I have a few trapdoor snails that have been in there since the beginning last year. Bullfrogs and painted turtles visit from my farm pond. Lots of frogs on both ponds right now.
Yes, I checked all the water readings, even got new test kit to be sure, as my other kit was 2 years old, and ammonia and nitrites were zero (still are) and nitrates were between zero and .5 ppm. Ph remains between 8 and 8.4. I posted all of this on another thread, and any other ideas, and others were as baffled as I was. When this first happened, I turned on my huge air pump, and had it going 24/7. Then someone said if I didn't have any O2 problems last year with the extreme heat from June through Aug., that was likely not the problem. It had not been hot at all when the problem started. I don't treat my water, it's well water and doesn't need to be treated, which is good, because I've done 3 very large water changes, at least 25% volume, and no problems in fact the fish have gotten more active.
Most of the fish have been fine, showing absolutely no signs of stress. Just a very few looked sickly, and I put them in a quarantine tank (55 gal aquarium) with medicine called "General Cure" that was supposed to treat about 5 different types of illnesses.
So, now that you know the "whole story", what is your guess? I figure you're going to say I need more oxygen, but that was already talked about, and I've been pushing air for 2 weeks now, off and on, not on 24/7 like in the beginning. BUT, I am going to set up a fountain in that pond, so there is more splash and water movement, like I have in the koi pond.
BTW, koi pond has had no problems, and 3 koi in goldfish pond are fine and dandy, but then so are the other goldfish that didn't get sick. So, what gets to just some of the goldfish in a pond, and not all of them? That's what happened, and that's what is baffling me the most!