Fungi infections are tricky. Too cold and the animals metabolism slows down but the fungi does not. Too warm and the axie's immune system gets over taxed and the fungi goes rampant.
The reason I advise against salt baths for fungal infections is tricky in itself. The truth is what we in the hobby often refer to as fungus or water mold is in fact not actually mold, but a mold like protozoan closely related to slime molds. While called "molds" slime molds in fact are NOT fungi either.
This is why meulaca based treatments work and salt baths do not. The active ingredients in meulaca kill off the hyphae quickly. The salt does not. Additionally,the slow action of the salt causes the Oomycete to go cystic. In other words it switches to sexual reproduction and forms spores which then re-infect later.
The best defense against this sort of infection is to prevent injuries, maintain stable water temperatures and chemistry, and most importantly remove uneaten food and feces as soon as possible. No amount of filtration will prevent it.
Also, if you have multiple tanks, it is VERY important to quarantine nets , turkey basters and the like AND wash your hands with soap and water before working with uninfected tanks.
It is important to note that you should never use these treatments direct in the tank. They can cause cycling crash which will cause even more problems for your pet. It is best to quarantine the animal in a temporary hospital box. While the specimen is recovering, It is highly advisable in this instance to tear down and sterilize the filter system and replace the air stone. If you use a substrate, this should be removed, washed with untreated tap water and heat treated. Then again, if you are going to do all that it is wisest to just tear down the entire enclosure, sanitize, and then get it cycling again.
Experience shows me that this issue is most common in tanks with substrate, which is why my aquatic ambystomids have none. It is much easier to keep the enclosure clean with out it.