hopefully i can help, your pictures arent real clear but some of the contusions look like possible columnaris, some of the symptoms you list agree too, do a little research on the web about columnaris, google is everywhere, if that is the case you are sort of on the right path with the tetracycline, it does work but columnaris kills quick, if you feel that its likely columnaris, i would suggest treating with kanamycin, you can find it in seachems kanaplex and its an active ingredient in furan 2, its also safe with all good bacteria, plants and etc and easily administered, if thats not the case and you feel the problem is some other bacterial problem , kanamycin is a broad spectrum treatment that cures most gram positive and gram negative bacterial infections, it saved one of my gulper catfishes of the few i had when tetracycline wasnt as fast acting, if you also feel this may be the case i suggest lowering the temp, this is one of the few diseases that cranking up the heat would be a bad thing, not saying im right, but just trying to be of help i know how it is to lose exspensive fish
