south african cichlid questions

Hi,
I have 2 South African Cichlids, one Albino and the other Black (I
know there are more subcategories, but this is the basic version).
Recently the Albino started exhibiting labored open mouthed breathing
and would not eat, he has since died. All water levels checked out
fine after testing. This took place beginning to end within 2 days.
I'm very upset because i love my fish and this was the longest i've
ever been able to keep fish alive. I've had both for over a year and
this was the first problem I'd encountered. I would really like to
know what caused his demise. I googled almost every variation I could
think and rcvd feeback such as lockjaw and throat blockage, but
nothing really helped. Aside from giving the fish an autopsy, I was
hoping someone could tell me what happened?

Next: The Albino passed away this morning and it has been 9 hours
since his removal from the tank. Within the last hour my Black Cichlid
has started showing very high levels of aggression. ex: scooping rocks
up w/ his mouth and spitting them out, biting a coral reef that we
have in the tank and swimming rapidly. Let me mention that they were
both males. I expected some depression, but this behavior worries me.
I want to insure his health. Any advice?