thank you odd duck, i have a friend who's daughter works with horses and is friendly with a vet and have asked if they might help me. the cories in question are young fish that i have bred myself and i still have the breeding group in another tank that is not affected. in fact if i'd not had this problem the sick fish were at a size to be sold, but obviously i put that on hold. all other tanks with young cories in are fine, it's only the one tank and only the black cories in that tank. i've asked my friends daughter for minocycline, kanamycin or metronidazole if possible and await a response, probably after the new year now. i don't know how the tubbed fish are hanging on, 9 days now with all the stress, but the things you've all suggested must be having an impact and i appreciate it. thanks again and have a great new year. cheers ron.