Ahh, the wonders of Cyanobacteria.
It can be every color of the rainbow and take on many forms. A green/black slime on your sandbed is definitley a cyanobacteria problem. Therefore, it could be many things fueling it.
How much/often does she feed? Light cycle? Skim? RO
, or tap water? How much flow is in the tank?
loves high nutrient, low flow areas (aka: most of our sandbeds). Increasing flow, manual removal, and more frequent water changes/reduced feeding will help your cause.
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