Possible Ammonia burn - PLEASE help

Hi!

Three days ago (Tuesday) I changed my Axolotl, Calypo’s, substrate and did a 100% water and filter change. I dechlorinated his water with API Stress Coat and also added Prime Seachem, as I always have with his water changes. Everything was fine the night of the change and the next morning, besides that Calypso wasn’t wanting to eat, I figured due to the stress of the tank maintenance.
I worked all day Wednesday (6am-10pm) and spent the night at my boyfriends since it’s closer to my work, and I worked on Thursday as well. When I get home, so roughly 32 hours since he last appeared OK visibly, he was floating, his gills shrunk and white at the tips, his tail tip slightly deformed, cloudy eyes, and red veiny skin. His water was murky, there was debris all over his tank, and a lot of bubbles at the top of his water. I thought he was dead, and then he very weakly went up to the top of the water for air. I immediately scooped him up and put him into 100% new dechlorinated water and put him in the fridge.
I went and had the tank water tested after I got him tubbed and fridged, and it came back with 0 ammonia 0 nitrates 0 nitrites pH 8.6. I’m wondering if adding the ammonia conditioner could’ve given a inaccurate reading, and I’m not sure what would cause the pH to spike so high.
Everything I’ve read about all of his symptoms lead me to believe that he has severe ammonia burns. I need to help him, I don’t know what to do. Please, please help me.

no ammonia readings in the tank is odd but the symptoms sound like chemical burns of some sort.
ammonia is a base so it could be the reason for the high pH, do you use test strips or the drops? the strips are pretty inaccurate if that's what you have so it could very well be ammonia burns.

id worry about nitrite poisoning too if your tests seem off, an easy treatment to cover all your bases would be a methylene blue dip (it oxidizes nitrites/nitrates, detoxes after exposure to high levels but is a general antiseptic too) half the strength as listed for fish then after that back into isolation with something soothing to the slime coat, indian almond or black tea should help.

of course use your own judgement, if it was some other chemical that made its way into the tank this might not help. definitely try and get a second opinion on that water value reading, if it really was 0 everything somehow im at a loss what caused this irritation

Thank you for replying, KumquatSquats.

Since my post, I figured out what could’ve caused the problem. I purchased a “quartz” crystal from an aquarium store, that ended up being selenite. Selenite is a calcium sulfate crystal, and is water soluble. I’ve read that in water with lack of movement, the calcium sulfate will create hydrogen sulfite, which is toxic. I’m not sure if that’s what happened, but selenite also raises pH. When I saw the tank I was quickly pulling everything out to get to Calypso, and i don’t remember the filter spraying water or making noise when i pulled it out. So i am worried that with a 100% water change, his filter also stopped working while i was at work. Either scenario would obviously create horrible water conditions and I feel AWFUL.
As far as the testing, I tested with strips. I have since gotten a API master water test kit, which will give me a lot better of a reading. I unfortunately threw out the bad water, I definitely wish I had kept it so i could do more tests on it.
Calypso is still alive, but definitely still not doing well. I’ve been tubbing him with almond leaves (100% water changes daily), and doing a daily (10 minute) tea bath as well. I just bought some Methalyne Blue today, I’m going to give him his first soak and I hope that it helps him. I am worried, he’s a juvenile and today will be the fifth day he hasn’t eaten. I have tried feeding him his earthworms that he typically eats daily, some frozen bloodworms, and I also bought live black worms today and I’m going to attempt to feed him those.
I’m just worried about him not eating. I can keep working on soothing and healing his skin, but I don’t know what to do about him not eating.