Thanks Dells, we have had a bit of rain, but nothing excessive. I DID figure out what the deal is though. I took the filter apart, and there was about 1 inch of brownish grey sludge in the bottom. I drained about 90% of the pond, rinsed all the media in old water, cleaned the gunk out and refilled. It's still brown.

I guess it needs to filter thru? I dunno. I miss seeing my fish!!! On the plus side, I found 2 more frogs.