Dark belly?

[mojo124]

Hi I recently became a first time axolotl owner, I got 2 axies, Mojo and Goob. I'm a little worried about Mojo, I've noticed his belly has gotten darker than it was a few days ago. He has a very fine sand substrate in his tank and I feed him earthworms cut into small pieces so he can eat them easily. Does he look healthy to you guys? If not what should I do??

 

[Tarabull]

The picture didn't attach. How big is you axolotl? It could just be the dirt that the earth worms are eating that looks black in its stomach. As long as its stomach is a normal shape, it's pooping, and eating fine I wouldn't worry.