Aggressive platy?

[Lexi B]

I've got a betta paired with a group of platies in a 20 gallon long. He seemed very chilled out and got along well. Except for with the only male platy. The platy chases and tries to nip at the betta, which is not at all the issue I was expecting. The betta has no issues with fancy guppies, guppy fry, cory cats, or snails. 

Should I remove the platies and try a different species of fish?

I don't understand the reaction to the betta at all 

[Kirsten]

Sounds like the platy is trying to mate with your betta, which I'm sure your betta doesn't appreciate. Yeah, if you can, may want to separate them. Either put the betta in with the guppies he gets along with or put the platy somewhere else.

Me, I'd put the platy and guppies together with the snails since they'll all like hard water, and I'd put the betta with the cory cats since they like the same water (softer and close to neutral) and definitely won't bother each other. Maybe some smaller snails like ramshorns or one or two nerites in with the betta to work on any algae.