At this point I'd find some metronidazole, in the form of Metro+, or Seachem's brand, to treat... It's considered one of the better cures for dropsy.
It's very possible that you aren't totally irradiating the illness which makes it return, stronger than before.. If you kill out all the weaker bacteria, the stronger ones will have more room to reproduce, producing an immune strain that will be tough to beat... If you choose to continue with the maracyn do not quit treatment halfway through...
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