IMO, the biggest deterrent from mixing African and CA/ SA cichlids is far more diet related than any other variable.
IMO the only way that diet plays into the equation is if one is discussing SIZE of food, and the potential for some of the smaller fish to overeat, causing gastric upset. The formula/brand of food if chosen wisely, is IME a non issue. I have fed the exact same brand/formula of food to multiple species of cichlids, from all points on the globe. That includes carnivores, omnivores, and even fish classified as strict herbivores. Sometimes keeping all 3 groups of cichlids in the same tank, a total non issue, all fish did exceptionally well as long as one removed most of the more common stressors, mostly aggression from tankmates.
As far as water parameters, I tend to disagree with some members that state that water values are a non issue. For certain species of SA fish I would disagree. Keeping many of SA species in hard alkaline water has proven over the years to be a very real issue, and that includes tank bred non wild specimens. IMO, and IME this is why certain soft water species are more notorious for sucumbing to certain ailments such as HITH. To those that disagree, You might be interested in reading this past discussion, taking note of what myself, Matt (dogofwar) and Tom (Aquanero) posted in regards to water parameters and how/why they can affect many of the SA species.
http://www.monsterfishkeepers.com/forums/showthread.php?548799-HITH-lATERAL-LINE-DISEASE-IN-CICHLA
Here's a portion of what I posted, which partially summerizes my thoughts with regards to water paramaters & some of the HITH prone SA species.
HITH is caused by stress, and in a glass box stress can come in many forms, for many different species of fish. In the case of blackwater species I agree with both Matt, and Tom, in that those species found in acidic blackwater environments do not always cope well with various parasites/pathogens found in non blackwater environments. Why do some fish get HITH while others kept in the same tank, and fed the exact same diet do not? As previously stated there is much more than just pH involved, and even tannins, various other natural turpines and chemicals found in indigenous plant matter may not only keep the pH buffered quite low, but in some instances (such as Terminalia catappa aka Almond leaves) some of these various indigenous plant matter are also known to produce antimicrobial activity that suppresses both gram positive & gram negative bacteria. Take those species out of that "protective" environment, and introduce them to paramaters outside their ideal range, and a fish that comes under stress (of any form) is going to be open for invasion from any number of pathogens that it would not normally encounter in the wild.
Start with post #6 (posted by Dogofwar) in the discussion linked to above and you just might be changing your opinion on water parameters, and certain SA species. IMO it's best to keep the species known to be sensitive to HITH in a more natural soft water setting, with non aggro species, AND keep their water quality pristine.
YMMV
