Illness/Sickness: Strange bacterial bloom and injury?

Hello friends!
I'm new to the forum, and I joined up to try and get some advice for my axolotl! The first axolotl I've ever had, so i'm still a bit of a newbie haha!

I got him a few months ago, the tank was cycled, he was healthy and, although it took him a week or so to eat, he was now eating like a mad thing! I managed fatten him up so his head and belly were the same and he looked healthy, never showed a sign of stress.
Then a week ago the water went a little yellow so i assumed i needed to replace the carbon in my filter, and I also ran out of water conditioner (I use regular API) so i popped down to the pet store. They were out of regular conditioner, but had a amphibian/newt/turtle one. I googled and asked and it seemed fine so i got it.

Anyway, I got home and started using it, and suddenly there was a bacterial bloom. I'd had one in a fish tank so i wasn't too worried about it but i checked the ammonia, which was at 1ppm! I did a water change, and it went down, but continued to be cloudy for a few days so waited a bit, and kept checking, then one night the water was significantly cloudier, axie seemed stressed (gills forward for the first time) and it was at 4ppm(!!!!!!!) I had read to get the axolotl out so i got a small spare tank and put him in there. I noticed that the ammonia seems to have burnt away a small angular chunk of his tail, and it was red and veiny. He didn't eat for a day, was not interested at all.

Today, I got the usual water conditioner as i think it was the cause of it all. Axie doesn't seem stressed, gills back, tail not curved, eating (yay!) and his wound seems to clean and not fluffy. I've been doing 90% water changes in his tank and he seems okay.

A few questions after that info dump (sorry if its too much info haha)!
1) What is the best course of action returning his usual tank back to normal? What % of water change do you recommend?
2) Is there anything I should do to ensure his wound heals well?
3) I hear people say '100% water change daily' when the axie is in a temp tank, but how can i do that with him in the tank?
4) He's currently eating 1 mealworm and 1 bloodworm cube/heart cube a day, he looks to be a healthy weight (I got him quite skinny but he's nice and chubby now!) but i hear people saying to feed adults every 3 days (he's definitely sexually mature, little black toe tips). What do you guys recommend?

Thank you sooo much for all your help! Just reading over this forum has been a huge help in getting used to my new friend

So, good news, the ammonia levels have dropped from 4-8ppm to .5 in one day very happy! Going to make sure its 100% clean and ammonia is at 0ppm until i put my axie back in.
Still looking for help on the other questions
Thanks!

Keep an eye on the parameters. If you get more spikes in ammonia or nitrite it may be best to remove the axolotl and do a fishless cycle and move him back in once it has finished cycling. If you do need to remove him, a Tupperware tub may be easier than a tank. If you have two set up next to each other, you can do 100% water changes by just transferring him to be he second tub, then disposing the old water from the first tub and refilling with fresh dechlorinated water ready to transfer him into the following day.

Be careful with mealworms. These are not suitable as a staple diet. Axolotls can have difficulty with the hard exoskeleton of the mealworms and if fed too often they may become a bit constipated. I would opt for earthworms as a staple instead. Mealworms are ok as an occasional treat. You can monitor how much to feed him by looking at his body condition. You want to aim for his belly being as wide as his head. If you notice his belly is becoming wider than his head you may need to cut back on how often he is fed. I feed my two every second day.

Keep an eye out for fungus but as long as the parameters are in check (try to keep ammonia and nitrite below 0.25ppm) he should hopefully recover. You could offer a black tea bath to help soothe his skin.