Do not use melafix, just keep up the salt baths. Don't use any chemicals if you can possibly avoid it, and then check whether it's amphibian safe (there is a checklist on axolotl.org) - don't trust a fish shop on chemical safety.
If you are going to fridge your axie keep it fridged. Did you go through the fridging tutorial? The constant changes in temperature is bad for them, you need to keep them at one temperature - either fridged or room temp. When you are ready to put your axies back in the tank after being fidged you need to let them and their tub come to room temp gradually before putting them back in or the sudden change can shock them.
Some axies won't eat when they are fridged as their metabolism slows down, and they may not eat for a day or 2 afterwards. Offer them worms, but don't be surprised if they ignore them.