DO NOT dose anything with axolotls, they absorb chemicals very easily through their skin and it can damage their livers and other organs.
DO NOT use melafix as it is liver toxic to axolotls.
If you need ANY help with your axolotls I would suggest going to http://www.caudata.org
and posting there
DO NOT dose liquid CO2, this can be toxic to amphibians
even using CO2 can be dangerous with axolotls as it can cause a shift in PH
additionally the amount of light needed for a well planted tank that needs CO2 would be much too high, axolotls are sensitive to light and cant close their eyes
It is always recommended to avoid adding any additional chemical to an axolotl tank
Do a complete water change and keep an eye on them
Theyre amazing healer and can even grow back sections of their brain so their gills should grow back with clean and cool water
Axolotls need water temps of 68 degrees or lower