Well the answer your going to hear the most around here is NONE!
But to be completely honest, I would say 4 tops 1 male and 3 females, but that would be pushing it.
I have 5 2" juvie Mpimbwe in a 55g and I feel bad for that. So its all a matter of how you feel about it I suppose. You could most likely "get by" with 4 in a 75 when fully grown but that would really be pushing it.
Thx for reply and honesty, and yes I know it was a pushing point, I was just curious to what it was. But LFS has (4) 3.5in juvies in a 20g, and I really think that is wrong, and he has had them there for 3 weeks now and offered me an really good deal becasue he cannot sell them, and I have spare 75g right now, so I guess at the time it just seemed right to get them out of there, and later get an 150 for them, just timing is not right for me to get 150 right now.
i have grown fond of bigger tanks, for bigger fish, but years ago bred burundi in a 48x24 80 gal tank. the ratio was 1:2 with a total of 6 fish. the biggest male was 10", with a forehead the size of my fist, and no fish ever looked stressed out to me (good appetite, no fin damage, no sunken belly, all but one female producing).
substrate depth, water change volumes, quality feed choices, and sufficient mechanical filtration, are all important considerations to help big fish stay well in 'smaller than suggested' aquariums.
4 fronts, the size you are considering, can be kept well in a 75 for a few years, IME.
I keep 6 adults and 6 juvies in a 125 at this time. Works out perfectly. I think I'm gonna have to get rid of the largest male when the juvies grow up to be males as well, though...
See how it turns out, but I don't think that it's impossible to keep what you are suggesting, if you keep up the water changes etc.
Once again I thank you all for you post they were very helpful in me making my decision, I do plan to get the juvies, and I plan to move them out of 75g by adult size time to something bigger to accommodate. :thumb: