is he in his tank or being tubbed, if in a tank full water changes have the potential of damaging the bio-filtration and therefore the cycle, only change max 50% per time.
what are the water parameters (I expect all the nitrogen compounds to be around zero due to water changes but it is useful to know ph kh gh and temperature)
your axolotl has what looks like saprolegniasis which is a fungal/mold infection (not to be confused with columnaris which tends to infect the gills)
use 100% holtfreters + 0.2g/l magnesium sulphate (use 3.5g/l non-iodised salt until all salts/minerals can be sourced) in the water he is housed in, give baths daily 10-15mins methyline blue + acriflavine (both mixed together half fish dose) the area of infection can also be treated by swabbing with potassium permanganate.
100% holtfreters is.. 3.5g/l non-iodised salt, 0.1g/l calcium chloride, 0.05g/l potassium chloride, 0.2g/l bicarbonate of soda.
lthier. Any advice would help (photos below)