Having all these mystery issues and a sick fish in my synodontis tank makes me want to be more prepared when my plecos fall ill. As far as I know, the plecos are doing wonderfully right now...but so were the synodontis before some mystery factor came into play. So to be clear, I don't think I have any sick plecos, just want to be more prepared. Good water didn't prevent my synodontis from getting sick so not counting on it to prevent my plecos from getting sick sometime either.
It got me thinking, what are the typical signs of a sick pleco?. I realized, more so then the synodontis, I think they could get sick un-noticed and die before I could treat them due to their normal behavior of hiding. Someone mentioned they stop hiding as a symptom of illness. If so, that would be a useful clue.