Platies
 

I have two male Platies in my tank and they are fighting. The people at Petsmart said that it doesn't matter if they were male or female ( I chose male because I like the specie and I don't want babies) they will get along fine. Now I'm thinking about returning both of them.

Hi Marko :D what seems to be the problem thou ?

Often platties sold in pet stores are crosses, or at least have some swordtail in them. Swordtails can be more agressive and this can be where the platties these days get it form.

How badly are hey fighting? If they are stressing and hurting each other than take one or both back, if they aren't bothering each other too much they may be fine. Try adding plants and hiding places as sometimes it's just a territorial issue.

It isn't serious but noticeable. The larger one creeps up on the little one and nudges / nips him. The little one then swims like crazy and does laps around my aquarium while the bigger one watches. Around 10 - 20 minutes later, it happens again.

Or you could add 3 females =)