I'm sure it's not a problem, but just to be sure, what are your nitrate readings? Cyano
comes from a few things....
Low flow (so make sure you have flow directed at the sandbed). Even in tanks with high flow, it's still possible to have dead spots if the flow isn't directed correctly.
High nitrates (they kinda feed the cyanobacteria)
Old lights (which break out of the blue spectrum over time, which can cause growth)
With all that in check, you can try adding something to keep the sandbed surface disturbed like...hermits or nassarius snails. But that's more a band-aid fix at the moment.
EDIT: Just noticed you edited your post after I responded.
Dead and dying algae can be a cause for nitrates as well, as it decays in the tank. A reading may help.
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