Can anyone help me figure out what is wrong w/ my fishes tail?

I have a male hi fin platy that is having tail issues. I'm not sure if its bacterial or fungal. It all started the begining of August. He was bullied by another male platy and got a bite taken out of his tail on the top corner. I got rid of the bully and waited to see if it would heal on its own. About 3 weeks later I noticed that on the bottom corner of his tail it looked lighter gray (his tail is light black/dark gray) and appeared to be shedding white %26quot;slime%26quot;. I treated w/ melafix for 7 days and no change. I waited 3 weeks and treated w/ API t.c. tetracycline for 4 days. I waited 2 weeks and it was getting worse and the bottom corner of his tail was wearing away. I assumed this whole time it was fin rot and was using meds that said fin rot. So then I used melafix again but this time for 14 days in a row ( I did a water change on day 8 and re-dosed that day). After 14 days his tail looked alot better. The color was back to a darker color and there wasn't any %26quot;slime%26quot;. But after 2 water changes (one done on the last day of treatment 20% just water and then 6 days later a 25% w/ vac), his tail started looked bad again, paled out color and %26quot;slime%26quot; again. So I picked up some maracyn plus and started dosing w/ that. I'm halfway through that and no change yet. Does this sound like anything you've came across? Is this fin rot? Is there a better treatment out there for this? Is it bacterial or fungal? I'm at my wits end cuz nobody at the pet stores has any clue what it is except that it's seems closest to fin rot. Sorry so many questions but I just don't know what to do. I test my water weekly and I have even been taking it into the store lately and it tests fine. I do weekly water changes of 25% w/vac and I really watch how much I fed them so I don't think I'm overfeeding. I know he isn't getting picked on by the other fish either. Please help, I don't know what to do. And please no mean or nasty comments, I just want some advice.Can anyone help me figure out what is wrong w/ my fishes tail?
This is almost definitely fin rot. There are many symptoms of this, and I would recommend this website:



http://aquamaniacs.net/forum/viewtopic.p



Just the first bit of it. It's informative and thorough. Anyway, as someone has stated previously, aquarium salt is a good way to treat fish diseases, but it is more effective when used with slight heat. I would also recommend that you change back to the Melafix again, as this seemed to work after 14 days.

Did you continue using it over the two water changes? With most fish diseases, you need to continue treatment until preferably a week after there are no signs of the disease left, as an extra precaution.

Any fish disease can easily return if not kept on treatment for at least 3 days after all signs are gone.

Hope this helped and I hope your fish gets better soon :).Can anyone help me figure out what is wrong w/ my fishes tail?
it does sound like fin rot.

instead of using all the chemicals, you should add aquarium salt. one tbs per 5 gallons of water. for future reference, if the first two full treatments (from either the same or different medication) don't seem to work, add aquarium salt and up the temp (around 79-80 would be fine) wait a few days and see what happens. that will help your fish cope with stress and create a new slime coat. it will also change the environment for the bacteria/fungi/disease and make it hard for it to live. so your fish will heal faster. along with the salt treatment, get something for the fin rot. and he should be fine :) good luck! :)