They are different, tetracycline is most effect against aerobic gram positive bacteria were as nitrofurazone is more effective against anaerobic grame negative bacteria (aeromonas infections) which I suspect this is will not respond to tetracycline. Triple sulfa, neomycin, kanamycin or even maracyn 2 (minocycline) would have been better choices. Tetracycline is not the correct antibiotic and is of very limited use when dealing with aquatic bacterial infections most of which are gram negative.