[Raul-7]

This is most likely due to some sort of internal infection of the gastrointestinal tract (commonly bacterial, sometimes parasitic). It's almost the equivilent of diarrhea. In many cases, it resolves on its own (just like it can in people) without medication... if it is eating and still swimming normally, I would just do water changes and leave it alone. If it comes with other signs like not eating and hiding all the time, consider quarantine and treatment with antibiotics.

I recommend you use GarlicGaurd and ParaGuard...Good luck!