Hey everyone, new guy here, stumbled on your forum while trying to get some answers on the web.

My Betta had a small body wound, not sure from what, and from that, in less than two days, it has grown about 500%, and now has what I think is a fungal puff around it. (Looks like cotton) He is doing very bad very quickly, and unlike the other tropical fish he lives with, I'm unsure about doing things like salt baths, melafix, maracyn, etc.

I'm not optimistic he'll make it, but I hope someone here can give me some advice.

I have included a very quick picture, but it doesn't show the extent of the cottonesque growth.

If somebody called Wilder turns up here, listen to her. She's saved more of my fish than I care to count.

I can't see the photo (I'm sneaking onto the net at school again) but cottony sounds more like columnaris than fungus. Columnaris is bacterial, and yes, it is very serious. Less virulent strains of columnaris can be cured with tetracycline which is usually readily available. Tetracycline-resistant columnaris is so tough and fast acting that it's virtually impossible to kill it. Google columnaris because I can't really help you much more with it without seeing the fish or the photo.

Whether it's bacterial (columnaris) or fungal, a water change and some salt won't hurt and could help. Change as much of the water as you possibly can, add new treated water at the right temperature and add 1 1/2 teaspoons of salt for every gallon of water in the tank. This is not an excessive amount of salt, one of my bettas has been in salt at this concentration for almost a week (bad finrot) and it does not bother him.

Some funguses can be slowed or killed by increasing the temperature but I think this will speed the progress of columnaris so I'd leave it how it is.

fungus can be "cotton wool like" so could well be fungus too, especially as it tends to infect existing wounds, which you said he had first.
is he still in the main tank with the other fish? if so i would get him into a hospital tank (heated) asap. you don't want the problem spreading to the rest of the fish.
if it is columnaris, its highly infectious, so treat the main tank with antibacterial meds to be on the same side.
the original wound may have been caused by a run in with other fish in the tank (maybe) what is he normally kept with?

Thank you both for the swift replies. Sadly he did not make it through the night. He looked a lot more peaceful than he had during the day.

Any suggestions on places to rescue a betta from? (I.e. he'll live in a 90 gallon unlike the little plastic cup they put them in.)

This was my second betta, the first lived about 3.5 years. Sadly this guy didn't last much longer than 6 months.

sorry i have bettas too and its not that you did anything wrong but betas dont last more that 3 monhts without certian aspects that need to be aquired and im sure you had these things but this stuff happens

What on earth are you talking about.....only 3 months

Well said Netty Op just said that his first betta lived 3.5 years and second 6 months, I just dont understand what are you trying to say I love bettas