You can tell the two diseases apart "fairly" easily. Usually though not always, columnaris will have the sign of fungus on the mouth, fins or across the dorsal like a saddle, it is often referred to as saddle back disease. NTD the fish go very pale and as the disease progresses you see little pimple like lesions under the skin in the muscle. It is really obvious when you have a fish who has it. I agree though that columnaris is far more common.Redshark1 said:Therefore we as hobbyists will not be able to differentiate between Columnaris and Neon Tetra Disease by eye although we might expect Columnaris to be the more prevalent and more deadly pathogen.