Dang it!
Sunday morning, the fish were fine, swimming and flipping around in the pool. Last night they all turned up dead.
The only correlary I can find is that there was a lightning storm the night before each group croaked. Dunno. I'm going to call the petshop today and see if they'd do an analysis of my water to see what's going on.
Sheesh. Good thing I still hadn't named 'em.