Fortunately, I live in Pacific Northwest like you, where we get plenty
of rain in the fall, winter, and spring, and the pond has a nice
overflow, so I think we've been getting some water exchange that way.
======================
Rain, containing no minerals, will soften your water, washing out your
buffering capacity and lowering your PH. Check after a heavy rain.

I often do. Yup, washes a bunch of minerals out. I have to keep a
close eye on hardness during the rainy season.

We can't use the pond vac in our ponds because one pond is too deep and in
both, and the "stuff" at the bottom clogs in the hose. If these vacs work
for you - more power to you! :-)

So far the Pond-o-vac is being temperamental. I'm hoping we just have
to get used to each other.

Joan