Look into keyhole cichlids also....they are not very colorful but in my experiences are gentle. Angel fish as mentioned above would be good too and or Kribs..
With any of the cichlids....if you end up having a pair, and they want to spawn there will be some nipping going on at least
And I strongly recomend that you use NO chemicals to alter your water parameters(Ph). It's a full time job for water changes, to be sure your PH remains stable....and one big mistake on a major
water change can be deadly....not good for a fun community tank.
Keep up your research and recomendations from the forum members and you will find a fish to fit your needs/wants without altering your water.