Oh! When the two guppies were with my betta, I noticed that my betta had a tiny hole in his ventral fin, and one of the pectoral fins and the bottom of his tail were slightly frayed. At first, I thought perhaps my betta might have fin rot or some kind of bacteria, so I did a PWC. The tiny hole healed/closed up very quickly, by the next day. I saw that the damage did not get worse, so I knew it couldn't be because he was sick with something. The pectoral fin and tail took a little bit longer, but they are all grown back now. I realize now that the guppies were nipping at my betta, too, but if I left them together, I knew my betta would cream both guppies in no time. Both guppies are very healthy and active, but one in particular got quite large (for a guppy) very quickly. Even so, he was scared to death of my betta. The two guppies and betta are much happier living apart!
Lesson learned just in time . . . before I "lost" anybody and before anyone lost any more body parts!