My dear Pat,
What you have been doing is on the right track. All the while, you have used metronidazole and trinidazole and these are effective in eliminating different strains of flagellates.
So, from the start of my input into this thread discussion, it seems we are already embarking on the likely cause. So don't be too worried with new inputs (though all are here to help you)....as they can be grouped up and treated with the same drugs you have been usng. Anyway, whether it is Trichomonas, Cryptobia, Tripanosoma, Bodomonas they are sub-group under the huge Flagellate family....like the hexamita and spironucleus.
The only difference is that the first set of flagellates may require extremely high dosage of metronidazole or other drugs like Trinidazole, Dimetridazole and Gabbrocol while the second set is most susceptible to Metronidazole treatment.
So Pat, the trigger of the gun is in your hand. So far, we have been doing well. The trial with trinidazole may not be effective due to many reasons.....dosage....like underdosed?..........Unable to dissolve .... like in metronidazole requires lukewarm water to dissolve before pouring in?.....Even having treated appropriately, still continue to feed freshwater aquatic animals like black worm so on, feeding them infested freshwater fishmeal and so forth?
Pat....please remember that too many random drug use and without the proper dosage can kill your discus in the long run. The liver may be destroyed before you know it. The choice is in your hand....in your finger I mean (^_^).
Take care and all the best!
Andrew