search on here or post to the fish purchases sticky.
i dont know how large your system is, but i have read more than a few times that 2 dartfish of different species (i.e. one purple, one red) in the same tank can be kept peacefully, especially if added at the same time.'
maybe someone else here can chime in, as i am not any kind of experienced with these...had one that kept jumping into the overflow *due to a coral beauty I believe) and eventually i never saw it again...its probably jerky under my stand or the baseboard heater....boo. was super bummed about it.