Oxytetracycline or OTC belongs to the tetracycline family of antibiotics. It works by interfering with bacteria's ribosomes, preventing them from creating proteins. It is therefore, effective against a broad spectrum of bacteria that infect fish.
OTC is against a variety of aquarium maladies. It can stop fin rot, a bacterial disease that attacks the fins of aquarium fish. Once the bacteria is killed, most fish will heal and regrow their fins in a clean aquarium. Oxytetracycline also treats dropsy or kidney bloat.
1/4 teaspoon per 20 gallons every 24 hours with a 25% water change before each treatment. Treat for 10 days. Remember to remove any activated carbon or Zeolite from the tank, since these materials will absorb the medication.