problem is that I am no expert, and I do not test the sand. Plus, I
have live plants in my pond so that must help my situation, along with
the skippy filter.

I agree. They likely mask what happens. Finally, the f-bed perhaps
repopulates with aerobes pretty quickly after it shuts down. Perhaps
for your situation, this is good enough.

I know my water is in great shape. I have it tested often at the LFS.
And I know it is overstocked in a HUGE way.

Intelligent pond management is what allows us to stock above nature's
levels. If you think your pond is overstocked, you should check out
intensive aquaculture facilities...

Anyway, if you happen to find anything definitive that states that
the aerobes in a fluidized bed have lifespans into days when the
device is shutdown, could you post a link to it here? I'm interested.

C//