Many apisto species do well in what's called a harem, and what I mean by that is ONE (1!) male and any number of females from 3-7. Odd numbers seem to do best for some strange reason, not really sure why. But only one male. If you are trying a breeding harem, you want to avoid A. njisseni and A. panduro, or those closely related. They will pair-bond more readily than other members of the genus and then will gang-up on the other individuals in the tank of the same species. Otherwise, any species will do.
Conversely, you can do a tank full of ONLY males, but you can only have ONE (1!) of each species, and they all have to have differently-shaped dorsal & caudal fins. So an example of some theoretically compatible males would be A. agassizzi, A. elizabethae, & A. panduro. Or A. cacatuoides, A. rositae, and A. baenschi. Or any other combination of species you have access to that have different finnage.
If these general rules aren't followed there will be hell in the aquarium until one kills the other. Or they beat each other to death. More or less.
YMMV, and a 75 might be big enough to negate some violence you may experience, but I wouldn't risk it.
Last edited by mrjbacon; 02-06-2019 at 10:47 PM.
Reason: added more info, and removed gibberish from when the cat walked across the keyboard