Originally Posted by Rod Hay
Part of the reason it is hard to answer this question is because there is NOT one easy answer. It really can vary.
Sometimes it will vary between individual males how much they are willing to share the aquarium. If you want both females and males I would not try more than two males w/ respective females.
Then besides the individual temperament of the males, there is the whole question of where the females will decide to put their nests. For instance, my male Pelvicachromis taeniatus "Moliwe" wants the nest under the Java fern that's at the far end of the tank. He even dug it out better for her. But MAMA refuses and always wants the clay pot next to the driftwood that's just slightly right of dead center. This causes Papa to boastfully patrol the whole tank. If Papa doesn't do a good enough job patrolling he gets a few stern reminders from MAMA! Junior can't "set up shop" w/ his girl because Papa is always keeping him tightly in the corner. . . . and so the story goes! This is a dwarf that mostly spawns as a dedicated pair.
Among my harem spawning Apistogrammas I've had an expert male that successfully kept the females in their safe separate ends of the tanks. Then I've also had females that have chosen to spawn within inches of each other and resultant fry stealing and lip-locking brawls. I've also witnessed both a male and female together gang up on attacking an unwanted female. I've also had a rare case where a male has attacked the brooding female and assumed the parental role.
Although smaller, always remember, even the dwarfs are never the less cichlids! Think. . . could I/would I house two mating pairs of Angelfish in a 55 gallon? If the answer is no; then the safest, surest plan would be to only put one trio. If you're willing to assume some risk then you could try out two trios, as long as you take some extra care to create a very dynamic environment. Actually w/ a larger fish like the Angelfish it's a lot easier to see if problems are arising. I've had smaller dwarfs be injured and not immediately know because they hide so well in a densely planted tank.
Personally, I think keeping only one species would be better than mixing them. My own older male A. cacatuoides is all of 4" long w/ a very big mouth! If he's in a mood not a single one of my A. trifasciata or tank strain A. agassizii Double Red could stand up to him. (They are safely in their own tanks!) If you really like a larger group I'd select one of the smaller more congenial Apistogrammas. IE., A. borelli and also A. trifasciata.
One other point. What are your water parameters? If higher Kh & Gh, I'd recommend staying away from the A. agassizii. They've been one of the species to give me the most trouble.
I have had a 50 gallon (same footprint just a lil shorter) with a trio of Apisto. cacatouides and a pair of A. sp. Inka 50. The male A. cacatouides beat the hell out of the male and female Apisto. Inka. So if your going to to go with apistos, its best to stay with one species. If you really get into them you can start setting up a few other tanks to accomodate them.
As far as species goes....I would go with Apisto. cacatouides or Apisto. borelli. They can accept a wide array of water parameters and they are a very beautiful compatible fish.