Until you know, the source of the organic material there really won’t be a fix.
I need to check something (actually with someone) before I give any advice on how to proceed.
My inclination is toward recommending a 10-ppm PP bath for your fish,
though if they are in a seriously weakened condition that could be fatal.
Believe me Shawn, woman is the most fiendish instrument of torture ever devised to bedevil the days of man.1
1Adjusted quote lifted from O Brother, Where Art Thou? (2000)