Re: So, you want a reason to not mix species?
I try not to get involved in these discussions. I have been into this hobby for only a short while and can be considered a noob at this point. I will only speak from my own personal experience.
Well.... Myself and two friends got into this hobby just last year.
I have a single species enclosure, a group of four Leucs. All seem healthy.
Friend #1 got 2 Azueres 2 G&B auratus 1 Luec and 1 Cobalt. He has lost 3 of his frogs since.
Friend #2 got 1 Azueres and 1 Leuc. She lost her Leuc. (competition for food)
There are many reasons why I've had success and they have not. I know for a fact that I did much more research than they did. I went with a single species enclosure because of the research I did. I know some of the other PDF boards deal with the same mixing questions as here and almost all mixing threads I've read were started by people with almost no experience.