Rummy Opaque Stomach

[Tinkertown]

I have 8 rummy nose tetras that have been in my aquarium for two months. All eating and swimming together. No visual issues with the other rummies. One rummy has a solid shape on the right side of its body. This can’t be seen from the other side. None of the other fish in my tank (8 rummies, 18 embers, 12 Pygmy cories, and cherry shrimp). 
 

it has had the shape since I bought it two months ago. Since then, it’s grown and darkened. I reached out to the LFS I bought it from and they suggested it just ate dark coloured food. I’m thinking that’s unlikely because none of the other fish have it and they all look ok. 
 

Any ideas what this might be and how to manage it? Thanks!

 

40 gallon long, ammonia 0, nitrite 0, nitrate 20, ph 7.4

shark pro 900 filter

[Colu]

It could be suffering from constipation have you notice it pass anything recently @Tinkertown

[Tinkertown]

No, I haven’t seen anything. Haven’t been watching too closely, but I also haven’t seen any long stringy poops either. Any thoughts on how I can help it move things along?

[Colu]

If it were constipation Epsom salt baths 1 table for 2 gallons for no more than 15 minutes for a couple of days as Epsom salt acts as a muscle relaxant am not 100% that what it is what I would is watch to see if he is passing anything for a day or two before doing Epsom salt baths @Tinkertown