Illness/Sickness: Incredibly confused on stressors and incredibly worried

Hi all, so I'm having an issue with my axolotl. I've had him for a week. I did small water changes every other day, about 10%, because I previously lost an axolotl due to over-feeding causing bad water causing fungus. The new water for the new axi is treated with Pimafix as directed by the man who I purchased him from. Yesterday I did a 100% water change because I rearranged the tank, and have been told 1 big water change a week is ideal. Upon returning little Itzli to the tank after a few hours I noticed what seemed to be his slime coat coming off. He showed no signs of stress, was eating, and looked pretty full and hearty. He was also pretty active. I decided to remove him from the tank and put him in a sick tank in order to remove the flakes he scratched off. They were all over. While in the tub, he moved less and less, his tail had curled along with his gills...like that of stress and running water stress... Which there was no current in the tub. All of the stuff that was flaking off has stopped, so I've returned him to the main tank.

The water in the tank and in the tub was/is about 62 degrees Fahrenheit. pH is 7.2, ammonia is 0.5, nitrite is 0 nitrate is between the first two slots on my API freshwater test kit so like 0.3ish?

He eats red wiggler worms, but won't eat them now. He pooped a whole bunch in the tub and looks so small now.

The substrate is slate with open spots of bare tank where the hide goes. I have a few plants that are potted, and a filter that I've rigged to reduce flow other than what trickles down the glass.

I'm concerned why he's stressed. I've also noticed his mouth is a tad open. He used to swim and walk around a lot and always follow the reflection in my glasses, now he just lays still occasionally flicking his gills like three times an hour, and looks sad with a curled tail and gills.

I'm confused because it happened when introduced to nice clean cold water, and then being moved to a tub with no water flow whatsoever.

Itzli is about 8 inches long. I'll provide before and after pictures. I'm hoping he improves in the morning and eats a worm. I don't want to lose another axolotl because I've followed every instruction given.

Note on ammonia: the level reads 0.5 straight from the tap, so I'm not sure how to lower the level through water changes. I don't know if I should try any conditioners or water treatments.

Itzli seemed to be happier in the tank with 68 degree water and a filter than the colder stiller water. ]:

Help is much appreciated.

Also, I'm not keen on fridging since the fridge here is at about 3 degrees Celsius and I think that help do my previous little guy in.

Please and thank you in advance.

The picture attached is him as we speak. I'm on my phone so I can only do 1 at a time. I'll post a few more of him currently and of him yesterday. I'll also see if I have any of the peeling.

More photos, still can only do 1 at a time from phone. Gah.
Profile view if him from tonight after I got done with work.

Yesterday

it's the ammonia.

Two or three days before.

Okay thank you, now how do you suggest I go about the issue? All tests have been the same since he arrived last Tuesday morning.

Collect water from elsewhere if you can or make sure you have Seachem Prime or API Ammo-lock which will temporarily detoxify the ammonia for 24-36 hours. Since large pwc's only make the problem worse...I would add a dose of the Prime every 24 hours (without a water change) until the ammonia stays parked at zero. After that I would advise small water changes done often instead of large ones less frequently. That way you're adding lower doses of ammonia, and the bio-filter should be able to consume it before the Prime wears off. Of course, if you can get another piece of established filter media...for now that will help reduce the ammonia level faster.

Maybe you should try leaving the new water out for a day or so, after adding the water conditioner, before adding it to the tank. Not sure what to do in the meantime though sorry

I posted this three hours ago. Woke up randomly and violently and found Itzli is dead. I followed all the rules I've been told by the man I purchased both of these axolotls from. Both of them only lived 1 week, but this guy was twice as big and twice as old. I think I'm giving up on the axolotl world for now. There must be something SERIOUSLY wrong with my water, and I don't even know what alternative I'd have. I'm responding in pure anger. The sadness will kick in in a few minutes.

Thank you everyone for the advice.

I'm so sorry for your loss ?

I am so sorry for your loss. Sometimes these things just happen, even when we do everything right. These guys can be so delicate. You tried everything possible. You sought advice. You did water changes. You treated your water.
I know you probably feel like it's your fault, but you tried so hard. It isn't your fault. Any number of factors could have contributed to your axxie's illness. I felt the same way when, after 4 years, my chinchilla Pepper died from malocclusion. I had been feeding him specially formulated food from the shop, and according to the vet, it was that which resulting in him losing all his teeth and dying - essentially trying to do the right thing.

I am sorry, but remember, everyone here knows what it's like to lose a pet and a friend. I understand your anger and your sadness. Let it out, you need to. When the vet rang me to tell me Pepper had to be put to sleep I cried for hours.

Sorry for your loss