3 inch long juvenile leucistic axolotl, might be sick? Help?!

[synchronicity]

Hi. I recently got two axolotls, a leucistic and a gray-black. They were doing just fine, but today I noticed that something's off with my leucistic, Wooper. His(?) stomach appears very bloated, there is mushy-looking grayish brown stuff in his stomach, and I see little tiny black/brown dots. He doesn't seem to be acting sick, but I'm worried something is wrong. Perhaps there is internal damage? It might be sand, but I have no idea how it could be in the very base of his belly without going through the lining of his stomach. Here are some pictures, they're a bit blurry but you can still kind of see what I mean. He is not floating to the top of the tank.. He hangs around there a lot, but he can swim back down and is able to stay at the bottom of the tank. His stomach is obviously puffed out, and I don't know what's wrong. Perhaps he's just constipated or something? I dunno. I am very worried about Wooper. Please help!


The first picture is him two days ago. The rest are all within the past five hours.

edit: I just took a really good picture of his(?) stomach. Here, have a look. It looks brownish, I'm wondering if maybe he IS constipated?