Jorm's got issues...(floating)

My beautiful wild type Jormungandr has had floating issues on and off for the last month. For a few days he seemed to be off balance and hanging out more at the top than usual, but after lowering the water level and changing the water more often with really cold water he got better. Now for a few days he's been the same again, staying very vertical, having trouble swimming regularly and not as interested in us as usual. I really hate to see him like this.

Here's the stats: Jorm is about 4 1/2 inches long, eating mostly pellets for his diet, but has had a couple earthworms. Water stays between 60-65 temperature-wise and has good levels in everything else. ph when I measured was about 6.5, I'm not sure on the ideal there though. He has a tank partner, Fenris, but they're still separated by a divider and FenFen is doing just fine, very healthy. They have sand as a substrate, really tiny and I've never seen Jorm eat any. Once a week maybe I can see where he's pooped, the last being a large amount 3 days ago.

I just put Jorm in the fridge as he seemed to be getting worse, really struggling to get into his cave where he can't float up, I'm worried about him and not sure what else I can do.

Have you noticed a difference between the days when you feed pellets vs. when you feed earthworms? I was feeding my pair of axies pellets and was having floating issues too, but since I made the switch to earthworms, no more floating. A lot of pellets are made with wheat or soy, things that axolotls aren't equipped to digest, so they end up getting extremely gassy. I liken it to what happens when a person who is lactose intolerant drinks milk. He/she doesn't have the enzymes to digest the lactose, and the result is the same: gas, bloating, discomfort, etc.