lost a monti.cap.....was it the sand???

[MitchM]

If your whole monti is sliming, then I would blame it on the xenia, but if the slime is only coming from the areas where the tissue is coming off, then I would blame it on the sand causing necrotic areas, as you and Jack already suggested.
I would up the water circulation to clear the slime away much more aggressively. It may grow back, if algae doesn't take a foothold on the exposed skeleton.

Mitch