I cleaned it with isopropyl alcohol just now, in case it's a fungal infection. Last watering was on the ~18th of last month, before it overwinters with little to no water. It's soil is a mix of extreme grit with a mixed shell of more normal soil around the outside. Terracotta pot. It gets exactly seven hours of bright, direct artificial light under a 200w grow light each day.

The only bugs around are a few fungus gnats that rode in on produce a few months ago. Any advice would be helpful! I'm trying not to carve into it unless absolutely necessary, as it's only about as tall as a pencil.