He lives in a 20 gallon tank with a Fluval C4 filter, and I change about 5 gallons out every week. During the change, I add freshwater aquarium salt, Prime, API Stress Coat, API Stress Zyme, and SeaChem Neutral Regulator. I keep his tank around 75 degrees F, but it raises between 77-78 when I do water changes until the water cools down. His parameters are all fine. I also am on top of changing out all of his filter inserts as recommended by the instructions (Carbon changed monthly, "Foam" changed bi-monthly, rinsed on a "non-change" month, and I rotate about 75% of the biological media every 3 months) I can't imagine the root cause of this would be poor water quality.
I read that another cause could be feeding outdated food. I currently feed Spectrum Community Fish pellets, which I've had for about 7 years (bought with my first cichlid). I'm curious if that could be affecting him?
Thank you guys in advance for your help!! I greatly appreciate it!