Story changed a bit. After I cleaned out the pond and got the pump running, I left the 5 remaining fish in there. I came back a little later and saw they weren't doing too well. They're all moved to a new pond now, but I tested their water and I've never seen ammonia levels so high. What could have caused that? They were at 0 yesterday, but today they're way past the red zone...it's amazing those 5 could even have survived. Did someone put something in my pond?