I took the filter apart, as per miskairal's suggestion.  There wasn't any muck (thankfully.. I don't deal well with muck of the fish variety) but there was quite a bit of java moss, and surprisingly, a human hair, wrapped around the spinny-part of the motor device.

Oh, and.. just a helpful hint for yous guys.. don't pull that apart over your tank.  Especially if your gravel is black.. ...and, you know, there are pieces that might come off of it that are small and black and pebble-shaped.

I swear I just spent ten minutes with my nose an inch away from the surface of the water, searching for that piece.  BUT.. everything's okay and the filter is waterfalling with the best of them.  I also have to wonder if all that java moss jammed up in in intake tube (not impeding flow, but.. there) might have had something to do with the ammonia levels.

In any case, everything but that darnable "buffering capacity" is down.. not perfect, but a whole lot closer to normal.  We'll see if it stays that way.

All fish but the female look happy enough.. she still sulks, but even that isn't as bad as I've seen it.  The male's tail has two or three splits in it, but so far it doesn't seem to be getting worse, and it doesn't seem to effect his ability to move.