I have it in mine also. There are snails yhat eat it. High nitraites cause it. Their is stuff you can put in a carbon bag to help kill it also. You have to change it out evety couple days.
It could be cyano bacteria, scrub tank and clean rocks, you may have to replace the sand in the tank, lower the amount of light you have in the system.
It could be algea I would give them a call to see their recommendations on if a treatment or management change is needed
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