Hi there. I recently got some sumo loaches and some of them have been dying. They seem to be getting bloated and getting some red spots underneath. Tank has very good filtration and oxygen.
Tough call as with any new fish. It's an internal infection, but the cause could be almost anything or a combination of things, like internal parasites, travel stress, acclimation problems. All you can really do is treat with wide spectrum med and antibiotic.