if one is female then a male may pair with her and they will break up the relative peace in the tank though with a tank that size it probably wouldnt be that big of an issue, and i dont know of a purple jag i think you are thinking of the ones with blue on their fins and backs? those are honduran jags and only way to get one is for aquamojo to send some fry to rapps and you order them from him, you can tell male from female jags by their spots, males spots will break up into smaller "jaguar" pattern and female will retain big juvie spots, best bet would be to get several of each kind when they are small and then slim down the numbers to the best looking male of each type that will give you the best shot of them all getting along