Axolotl acting weird!!!

I'm a new axolotl owner, and I've had mine about 3 days now.. for the first two days, all he did was stand around really not doing anything, but today, i tried feeding him and he threw up what i gave him and his food from yesterday! hes about 6 inches (15 cm) and i fed him almost a whole worm (nightcrawler) everyday. I read that happens if you overfeed.

The water condition is fine, but my pH is 8.5 and I'm not sure how to lower the pH. I am also concerned with him because he is swimming around a lot more high than he usually does and is having a little trouble staying at the bottom of the tank. His tail is slightly curved and i think that might be because he is stressed about not staying down. He also keeps swimming to the top and just swimming back down, i have an air stone in the tank so im not sure why he keeps going up. I'm just not sure if this is normal, since he usually sits around doing nothing. please help! thank you!

after some research, it was just him settling in the first two days and he also had to poop haha. I still don't know how to lower the pH levels though...

What is the pH reading for the water straight out of the tap?

Also, just be mindful to check the ammonia/ammonium level given that both exist in equilibrium in water and will favour ammonia in the presence of higher pH.