I would treat with Met as directed, just in case there's an internal parasite problem. Please DO NOT feed beef heart (or bloodworm) to these fish, they are very susceptible to bloat, and high protein food (as well as water quality) is a possible trigger, also mammalian protein (and the fat with it) is not good for long term health. Krill, gamma shrimp, mussels, veggie flake, algae wafers and a good quality pellet is a better diet for these fish.