PH Levels are completly irrelivent. 99% of the fish you find in a pet store these days are raised on a fish farm somewhere where they use the same water for all the fish. These fish basically have all adapted to the same ph levels. If you had wild caught African and American cichlids then yes I would be concerned about PH levels, but otherwise PH is completly irrelivent. While I dont have a mixed community at the moment, Ive kept Africans and American Cichlids in mixed communities for YEARS and years togeather with zero problems. As long as your africans wont fit in your O's mouth you will be more than fine.