It is difficult to manage the chemistry of your pond water when you have a high rate of water passing through your pond.
Having TOO MUCH water is a much better problem than not enough.
Can you install any kind of gate in the feeder creek and divert water around your pond on most occasions?
If so, then you might be able to do affordable amendments on your pond.
Also, the pine needles going into the pond are certainly adding nutrients and increasing the muck buildup on the bottom. Clearing back some pines sounds like a good idea to me.
I believe the green pine needles probably also lower your pH (and worsen your water quality), but I am not sure on that one.
I have caught bass in forest ponds that had so many oak leaves that the water was permanently stained brown. Didn't know the pH, but it had to be low. You making improvements can only help your pond get better from here.
Good luck on your new (to you) 4.5 acre pond!
