Looks bacterial or viral to me, could be HLLE if its been growing a while, or could be columnaris if it came on suddenly (the white tufts are similar to some colomnaris symptoms (if that's what I'm seeing in the photo)), or even Lymph a virus (if it is, there is no treatment except lots of clean water.
I was in Colombia about 2 years ago, checking out the Magdalena river system.
Since the water is flowing down from the nearby Sierra Nevada de Santa Marta mountain range where Umbi's live, it was quite cool, even near the sea, only in the mid 70s'F, I was surprised at how cool. Their habitat is a sandy bottom, around submerged logs and rocks
If your tanks temp is in the 80s, this might indicate columnaris (it is most virulent at temps of 82'F and above, and a tad on the warm side for the Umbi.
They also inhabit rather fast flowing waters, which are practically zero in nitrate (I test water parameters of wherever I go, pH nitrate etc), so if it were me, I'd be doing enough water changes to keep nitrate in the single digits.