all male school?
 

I want to add some cpd's (celestial pearl danios) to my 6 pygmy cories tank.
Can I get just males (assuming they can identify the just part) to keep them from fighting? or will they fight more because there are no females. Our tank is a no tolerance to violence tank;-)

All members need to get along amicably-the aquarium is a nano eheim 6 gallon tank-
Thanks for the help!

I'm not sure about the fighting, but if I were you I'd only keep one or the other and a snail or two in a 6 gallon.

They like to be kept in groups of atleast 6. Due to the fact that you already have 6 fish, I wouldn't add more. Also, remember the "Rule of thumb" 1 inch of fish per gallon.

As for the sexing, the females will be duller, with a paler red. They will also be "chunkier" than males.
The males also have orangey stomachs and have black bars on the anal fin unlike the females.

I would not add anything else to that tank otherwise you will overstock it. It is too small for anymore fish and even a bit small for your current ones.