Gotcha, yes, Skippy does not recommend cleaning the media or even touching the filter at all. I think there are some folks on this site that just flush the barrel, but don't touch the media either and they have clear water. A pond in direct sun all day is truly a whole different ball of wax, for sure. It has added stress on it that other ponds do not have--and green water can be a common threat in these locations.
I do clean my media once per month with a pond water rinse in a bucket. Have never had any problems with my bacteria colony and have crystal clear water. My pond does does not get morning sun, but gets sun all afternoon. My old pond was the opposite, and I got early morning sun only and then it was shaded most of the afternoon.
Give your UV a chance to so some more work and try a bigger water change. I look forward to hearing your results in another week. it does sound like you're on to clearer water....
What size is that filter on that 3000g pond you've got there, by the way? And how long has it been running on your pond? Sometimes if a filter is too small, you can get clarity issues too.