Sorry for joining your discussion, but I have the same issue. I bought today 2 Agassizii Super Red Apistos. One is a definite male, but the second one ... I am confused. It is less coloured and sized, but it can be just young. Please help me as well 
You need to take it out of the tank as soon as possible.He is chasing the small one really hardThe small one is quite black and under stress.
I don't know, it would have been similar parameters to yours. It is meant to be temperature dependent, and 26 - 27oC is supposed to give 50:50 male : female. I only ended up with 4 or 5 fry, so it may have been survival of the biggest.Any thoughts on what caused 100% male ratio Darrel? My last batch was same at 25.5c, ph6, tds under 100ppm.
Ade.
I'm really not qualified to judge, hopefully some-one else might have a better idea based on the videos.The question is still open... do think my small fish is the non-receptive female or young male?
I understand that you want a definite male or female answer, but I can't give it. Sorry.