Sorry to hear your axolotl is not too well.
Firstly regarding the fridge ( appologies if you all ready know!!) , the water needs to be dechlorinated. The water temperature should be no lower than 5 degrees and back up bottles of dechlorinated water could be kept ready prepared in the fridge too ( means the temeprature of the new water will be more stable for the daily water changes.). You will need to do daily water changes whilst in the fridge. I personally would offer food, but if not eaten in a reasonable time (i.e an hour or so) remove it so it does not foul the water.
He does sound like he is having problems with the water quality. Are you able to test the tank water for ammonai, nitrate , nitrites ? If not take a sample to your local pet shop and they will usually check it for you.....resist all attempts that they mau make on persuading you to purchase 'cures' as these may cause further problems.
Generally the axolotl tank need to be kept ideally below 20 degrees ( higher starts to stress them ( much like me!!) , 20 % weekly water changes with dechlorinated water and general spot cleaning of left over food and droppings also need to be done. I also do weekly / fortnightly water tests to make sure all is as it should be.
Hope this is some help.