I'm not sure if my paddletail is swimming normally

Hi! I just got my first paddletail newt a few days ago. I believe he's male, don't know his age, however he is eating well and moving around quite a bit.

I'm concerned with the way he moves around. Often he swims upwards but seems to sink before he reaches the surface. He tends to like walking along the bottom of his tank or simply laying there a lot, but when he does his body never seems to be straight. He's always curving, and sometimes it nearly looks like he has a hunchback. Here's a picture of what it sort of looks like.

He was housed with a bunch of Japanese firebelly newts at the pet shop he came from -so my mother says- so I was wondering if maybe he's sick or injured. Or is this normal? Could it just be stress related to his new environment- like tail fanning? Or am I just worrying too much about him? Thank you in advance.

PS- Sorry if this isn't the right way to ask questions. Like I mentioned: total newbie over here

Can't tell much from the photo. Some newts do arrive with spinal deformities/injuries. The setup should provide him with a small area to get above the water (and a secure lid, in case you missed that). If he's having trouble surfacing, you could also provide a submerged rock near the surface for him to rest on.

I'd done my homework about the lid and will definitely keep some submerged rocks in for him. I think that he's doing better now. In the pet store where he was found, he had barely enough water to cover him so I think that he simply wasn't used to having room to swim around (but it could also mean that he was treated poorly). As for his back, I'll wait and see but it doesn't seem to bother him. Thank you very much!