New 55 gal/48" tank for Cichlids

[AquaRon]

I started this tank for African Cichlids. Waiting for nitrates to show (day 7).
I have ,1 male/ 3 female (I think). Elec. Yellows, and 4 Elec. Blue Haps (sex TBD).
I would like to add a 3rd group of 4...am considering Peacocks. Are they too aggressive for the others?
If so, what other choices make sense?

 

[AquaRon]

No response on Peacocks.
I will try one other question.
55 gal tank started 8 days ago. Put filter media, gravel, water, 4 moss balls from cycled tank in day 1...10 fish, 5 live plants, 4 moss balls in day 1...
Ammonia always reads .25, nitrites 0, nitrates trace. Added Stability to filter daily, temp 83F, PH 8.1
Could it be tank has already cycled and plants are absorbing nitrates?