I agree 100% opcorn:why_spyder said:For the Cyno. sp. hara (white tops), I would go less than 5-7 if this will be a long term tank. These guys aren't one of the "dwarfs" of the Cyno. world.dielikemoviestars said:In a standard 4' 55, probably 10-14 saulosi (1:3-4 ratio) and 5-7 afra (same ratio) would work. Both species stay small so 20 fish should be no problem.
I don't see a problem with mixing Ps. saulosi and Cyno. sp. hara other than aggression. Some people have problems with aggression while others don't. Personally, I have yet to have an issue in this area but my fish aren't full grown either. My Ps. saulosi are still about 2" and my Cyno. sp. hara are in the 3"-4" range - and they are housed with many other species in a 100 gallon stock tank. When they were together in a 55 - they were smaller than this.