Did you quarantine the newest addition?
If not.... that's probably where the problem came in.
If the problem is bacterial, raising the temp can make the problem worse.
Besides high temps being stressful for the cichlids (especially rift lake species, because those lakes are very stable temp wise), many pathogenic bacteria thrive in temps of 82'F and above, and up into the mid 90s.
When I was working in a lab as a microbiologist, when we wanted to grow pathogenic cultures we would put cultures in a 95"F incubator.
But there is no way to be sure what the disease is, without a microscopic evaluation.