Have you tested you water about 15-30 minutes after feeding to see if you have ammonia spikes? The thing with an under filtered tank is that it will ammonia spikes after feeding due to not having enough bio media. I am not saying that your tank is doing this but I would test this theory if I where you to be on the safe side. Ammonia spikes can add stress which can in turn make any fish more apt to get sick for multiple reasons or just up and die. Im am curious now next time you feed or when you get a chance do a full water test after feesing and post results
I will have to do that. I think after 3 years I would have noticed something.
