Super fat Glowfish Tetra

Hi and welcome to the forum

How big is the tank?

Have you checked the water quality for ammonia, nitrite, nitrate and pH?
If yes, what are the results in numbers?

Can you post a picture of the fish?
If the image is too big for the website, set the camera's resolution to its lowest setting and take some more. Post a picture that clearly shows the issue.

Is the fish a Glowlight Tetra (Hemigrammus erythrozonus) or a Glowfish (https://www.glofish.com/) ?
If yes, how many do you have?
Tetras need to be kept in groups of 10 or more. If you only have a couple, they stress out and can become fin nippers or just chase other fish. They do this because they are stressed and are trying to hang out with other fish, but the other fish don't want them around so swim away. The tetras chase the other fish and it stresses everyone.

If you have a female Glowlight Tetra, they can sometimes get really fat from eggs. If there are males in the tank and the water is soft (low mineral content), the fish usually breed in plants and things settle down. But if there are no males or the water is hard (contains lots of minerals), the fish won't breed and she might become egg bound and will remain fat.

These look INCREDIBLY similar to my danios... perhaps I have glo tetras?? They swim all over the place, very active. I only have three of them, do you suggest I get more? I have 4 black neon tetras and only two guppies since one of my females died last night. 30 gallon tank. Currently working on getting my ph up using crushed coral in the filter. I'm at a 6 right now.