swimming upside down

how it started, I put it in a quarantine tank because of popeyes. as eye 'healed', move it back to the main tank. few hours after move back to main tank, spot it swim erratically, darting around the tank while body... not swimming straight horizontal. search similiar symptom, possibility cause...

Hey guys, I've typed up a very long message but it got lost when on image upload (my stupidity) so I'll make this quick. I've not been very successful as a pleco keeper and have lost maybe 30+ juveniles over the course of the past 4 years. I'd have some that I grew from 1" to larger but they...