GREAT IDEA .....NOT!!!!!!
Sorry but bettas will and have killed male guppies,especially the real fancy types with long flowing tails.I should know my betta Zeus has killed two of my guppies.This is what happened.......I bought a 55 gal. tank and I decided to let it mature,I introduced a pleco,an albino cory and Zeus,a beautiful blue male betta.Well,everything was going on just fine and I decided to purchase some fish,I went on line and got me some show quality guppies from Aquabid.At first Zeus didn't like the idea of having to share "his" tank,it seemed irritated having all these juveniles swiming around his domain.Anyhow,the guppies grew as so did Zeus.The male guppies started to grow these magnificent tails and Zeus still didn't like the guppies,especially the males.I didn't think much of it,after all Zeus couldn't swim as fast as any of the guppy and there was no posibility that he could catch any of them.Boy,was I wrong.You see, he was smarter than that;He waited until the lights were out and then he would strike.The first time I noticed something was wrong was when in the morning one of the male guppies was missing a chunk of its caudal.I thought maybe it happened swimming around some rocks.Well,two days latter I turned the lights on and I found Zeus chewing something,later I realized it was the tail of one of the other guppies.I then took him out of the community tank and placed him in a spare 10 gall.To this day Zeus still there with Pandi the cory and a bunch of neon tetras.Once again he's the master of his domain.