When to Terminate a Bath Treatment

No chemical used in aquaculture is completely harmless to fish. Treatments are designed to be more harmful to the problematic organism (ie. bacteria, protozoan) than to the host organism (ie. fish) which results in successful elimination of the pathogen with minimum damage to the fish. For some chemicals, particularly copper sulfate, the difference in chemical concentration which is lethal to the pathogen and that which is lethal to the fish is small. If fish show any signs of distress during the treatment (ie. trying to leave the water, gasping at the surface) the treatment should be terminated immediately and fish placed in clean water.
If fish are in a pond and have been treated with a low concentration of chemical (prolonged bath) there is nothing that can be done to remove the chemical if it has been improperly applied. Again, one way to help avoid losing a pond of fish by accidentally applying too much chemical is to have the amount of chemical to be applied calculated independently by two people. Volumes of ponds should be known and the amount of chemical needed to treat each individual pond should be calculated and recorded for easy reference. Errors are best avoided by preparing for a disease situation before it happens, rather than frantically calculating treatment rates and locating chemical suppliers when a disease is in progress.