Lou,
thought I'd weigh in on what I do and maybe it might allow you to continue the pond. I read most of the threads, though don't post as often, but still have had a lot of ideas come from here as well as see that the way I'm running my pond, surely does minimize the effort compared to others, which I sense you are looking for in keeping your pond.
A large reason for not having as much worry/work, besides the bog, is the fact my pond is enclosed and I get no predators nor leaf/debris.
So, for filter; I have a bog (bottom fed from a pump in the pond) and pond plants, and that is the extent of it. No maintenance, nothing but watching the bog help keep the water clean.
I have two air stones ( used to have one, but winter seems to like to shut down one line sometimes, here in Michigan) plus a waterfall and stream to help add oxygen.
My pond is about 2700 gallons (roughly 18' x 9' x 4', and can see the bottom), I have about 100 goldfish varying in size from 10" to 3", one small turtle, and two frogs. I feed about two handfuls of food a day, sometimes every other, and the fish are usually fat and healthy.
Now, I have never done any major water change, I do fill up often in the summer when it's hottest, maybe 3-4" at a time, depending, and have also never tested the water either. I tend to watch how the fish, plants, frogs, snails are doing and as long as they are acting normal, I figure all is well.
I have not had the dreaded green pea soup ever, though sometimes in the spring, the water is less than clear. Sometimes I get string algae but it seems to go away as the summer moves forward.
The only maintenance I usually do is groom the plants and lower the lilies in the autumn.
Winter; last year I used a pond breather and have a heater ready, just in case, to keep the pond open for off gassing. To date, I average maybe 3 fish losses a year and I'm assuming that's because they were weaker than the rest and couldn't handle the last two record setting season's cold.
So, not sure you can mimic this or even want to, but really, I rarely do much but sit and enjoy the fish. I hope you can continue because I know how it would be here, should I have to consider shutting everything down; not something I'd ever look forward to and I sense you'd like to avoid also.
Perhaps I've given you some ideas/alternatives and you can continue on even longer. At least I hope so.
Michael