females will get a pink belly when they are spawning...it'll actually be real easy to tell once they get to 1.5-2" ... Your going to run into problems when a pair match up and decide to have babies....they will take 50% or more of the tank and terrorize/kill anything that gets near there babies...especially the other con...Honestly from experience...once they start protecting fry...your other fish are not going to enjoy it...