First before anyone gives advise we'll need information of your tank size, whether you've cycled it, and water conditions ( ph, nitrate, nitrite, ect..)
Welcome! as paperdog mentioned, it really depends on how big your tank is and what the water chemistry is. Platys are generally peaceful and can live with quite a few other fish- tetras, cory cats, gouramis, guppies... the list goes on. More info would be a help!
Just wanted to know what other fish I can have with my three platies. Any info will be helpful! Thanks!
