I think you may have a couple of things working together. First of all you should have a quarantine tank that is not hooked up to your main system for new fish. That being said my guess of your secondary problems may be this. If you had a drip system that you turned down or off to medicate, than your filtration was unable to handle all the ammonia,This caused an ammonia spike which caused stress to all the rays. Then when you turned it back on the prazi was deluded and the old rays were weakened and the flukes could then take hold.
i know, im kicking myself for trusting a captive bred ray and not qt'ing him. but cant change that now.
i turn my drip off from time to time, and never had an issue. but i do think these flukes are the problem, and i think i killed some off, and they hatched or came back.
Things can happen very quickly overnight. Just because the numbers on a test kit indicate 0 at the moment does not mean it was at 0, three days previous. Sometimes rays feel the stress/effects of water quality change after the fact and not right away. Do you keep a pH monitor on the system? If so have you seen any fluctuation in the last few weeks?
Something else may be to blame here, for the lesions and such. However, I think sliding spots is a very good indication of water quality issue.
thanks for yalls help. it is not water quality.. another member got a ray from the same batch and he is fighting flukes too. but i questioned whether it was or wasnt as well, but what are the chances we both having issues?
thanks all i appreciate all the ideas!, tank is now treated with prazi again.... he is still eating so that is good. i may be wishful thinking but i think he already looked better this morning after 24 hours of treatment.