Follow up on this: After running my pump and tube in a bin with water and a little vinegar for a couple days, it tested negatory for ammonia. (yay) Should have done that when I swapped the pump from the old sump to the mixing bin. Lesson learned...
Since catching the issue, the water params are back to normal (no trace of ammonia or nitrates from the tests). I am doing extra water changes for the next couple weeks as a safety measure.
Now... I'm fairly certain that the small ammonia that got into the tank (from two water changes ago) has caused my anemone to stress. It's tentacles have shortened and almost all of them look pinched off at the ends. It still appears to be eating little bits of food. It's condition has been stable (though poor) since the last water change a week ago.
New question is: At this point, what's the likelihood of this anemone getting back to full heath (rather then continuing to decline until death)?
Also, should I spot feed it SMALL bits of food daily, or just leave it alone and let the clowns take care of it?