Not sure what it is. When it started it really looked like a nuchal hump but then a lot of swelling/ bulging at right eye area occurred.
Only thing I can think of is some genetic aberration causing this apparent "hump" edema, Popeye or a parasite disease.
Have doubts about a parasite disease because nothing new has been introduced into the tank in a year.
I have administered Kanaplex treatment (for Popeye) (1 week). The acara is acting normally and eats well. The bulging hasn't gotten worse.
All fish acting normally in the tank. Yesterday silver dollars were spawning. Tetras and acara were eating the eggs.
At this point just monitoring.