Karthik,
Given that the oxytetracycline did not show any appreciable results, perhaps the culprit for the infection is not a bacterium. It could very well be a protozoan parasite (Trichodina, Epistylus, etc.). If this is the case, a typical treament regime involves using formalin at low doses. I would encourage you to research the dosages needed as I don't have them memorized. Hope this helps.
