Guppys and Danios

Question
I have planted tank with danios, cory cats and otos.
Can I add guppies? Would it be ok to have just male guppies in with the other fish?

Answer
How large is your aquarium, how many fish do you have?

If you have ample room, guppies would be okay, but I personally would not just add males, because they CAN get aggressive if there are no females. If you really want to, you can try it, because it sometimes works...but try at your own risk.