Help! I can’t tell if my Axie is sick or I’m being paranoid!!

I’ve had Cthulhu for almost a month. I got him on the 10th of February. He’s gotten really big, really fast and was pretty big when we got him. He’s 4-5 inches long and he’s in a 20 gal. Long. I try to keep his tank between 60-65 degrees Fahrenheit. He was eating bloodworms but now he eats primarily Nightcrawlers every other day and pellets almost everyday. Sometimes I give him blood worms but not often anymore. I’ve been worried that I switched him to worms too soon. I also worried about him getting stressed due to poor water parameters. I’ve been fighting my parameters for almost two weeks now. I don’t think my filter is working enough for him. It’s for a 20, and was working fine until he got bigger. I’m working on getting another filter but the ammonia levels have been at the 1.0-0.50 range for a while. I’ve been doing partial (25%-50%) water changes for almost a week trying to fix it but it’s not working. I can’t tell if he’s sick or not. This is my first axie and I’m really worried that I’m not doing something right.

My thoughts: Maybe your over feeding, that could cause a problem like that, as a general guide your axies tummy shouldn't be wider then its head or its overweight how often do you feed.
I don't know what night crawlers are sorry, I don't think we have them here I just feed mine earth worms, pellets, blood worms and the occasional meal worm and fish.
Your axie looks healthy in the pic though if it changes or acts differently you might need to remove from the tank.

Can anyone else help here??

Thank you so much! Night crawlers are just a type of earth worm from my understanding. Everyone I talk to at pet stores around where i live say it’s the best for him that I can get around here. I feed him a whole worm every two days and a few pellets between. I will give him as many pellets as he wants when he acts hungry. It’s usually just a snack with a couple on the days between worms. I have a little plate in the tank that I use as a dish kind of. He goes and sits on it when he’s hungry and I feed him pellets then. His belly isn’t bigger then his head yet. But it’s getting there. I have a picture of it. I think I might just be really paranoid. Every little thing freaks me out and I read too much on the forums.