The friendliest place on the web for anyone with an interest in aquariums or fish keeping!
If you have answers, please help by responding to the unanswered posts.
You have a mbuna and an Aulonocara sp. (peacock) and this combo sometimes works and sometimes does not, even in much bigger tanks. They will definitely fight in a 20, so keep an eye on them. I am assuming they are juveniles?
if you have nitrites it may be throwing off the pH ... i find the pH will stabelize once your cycle is completely finished. Once those nitrites hit zero.. be sure to only add one or two fish per week!