Sounds very odd the way the guppies are acting. I also have a few stray guppies swimming around in my rbps tank that are now starting to breed. I believe that the ps are just used to them and dont see them as food anymore. Also I think that my ps are smarter than they seem. Why should they waste energy by chasing down the guppies when they know that they will get fed and not have to exert an energy at all. I tried not feeding them for a few days but they didnt bother the guppies. I might try taking the guppies out of the tank for a week or so and then put them back in one at a time. Hopefully they will eat them this way. Anyways good observation and good luck with your piranha.
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