I have found the Maleri (very similar fish) to be very hardy the only issues I have had are with aggression between adults or within a pair (female is very aggressive to male) but have my pair in a 2ft tank now and they are fine. They can be sensitive to water quality so making sure you don't overfeed and keeping up with regular water changes helps apart from that I don't know what you could be doing wrong to kill them. They don't need a PH at 8.5, 7.5 will be fine and certainly wont kill them, I sold some to a guy who kept his in mildy soft water with a neutral ph and they still grew up and bred fine..
I would be cautious about buying an adult pair, jullies are known for packing spats between pairs when you move them obviously there are ways to do it but at first I would add them to a tank with other robust cichlids so they have some fish to pick on together rather than turning on each other.