tetra with deep ulcer

Question
Hi Chris,

I have a tetra (bleeding heart) that has developed a large ulcer/lesion on its back, behind its dorsal fin. When it appeared that this wasn't healing on its own (at this stage it was getting deeper and started turning reddish/bloody) I moved the fish to a hospital tank and began treating with erythromycin tablets for 4 days as indicated, along with Melafix.  I've continued treating with Melafix, and am on day 5 of treatment.  Also doing 30% water changes daily, using water from the original tank, in which all the other fish are healthy and thriving.  This water also contains a low level of salt.  The ulcer is now a whitish colour, and I am not sure if it is healing or progressing deeper into the tissue.  Is there a way to tell if the fish is improving, or if it should be euthanized?  It is acting normally otherwise.  How long should I continue treatment before giving up hope that this fish will recover?  Thanks for any help you can offer.
(10 year old tank 35 gallon tank, 3 lemon tetras, 2 bleeding hearts, 2 black skirts, 4 corys, 1 standard/1 dwarf pleco, 1 female betta, 1 german ram, water parameters good, 25% water changes weekly, half and half with tap and R.O. water)

Answer
Hi Kim;

If the redness is gone and all you see is white tissue, it probably is healing. Especially since he seems to be acting okay. It takes a long time for the flesh to heal after such a serious infection. I would just keep using the Melafix and give him more time. Keep up the good work!

At Your Service;
Chris Robbins