hi,

how many gallon is your aquarium? And are you over stock? Check out the PH level for yr malawi. they do preferred high PH like PH7.8 at least - PH9. If you found yr PH level is low...try to get some coral chips and put inside yr filter. Coral chips will raise the PH level.

And other Malawis is fine? Normally cichlids will attack each other. especially the same breed. Dont over stock yr aquarium will do. provide them some space to hide.