Well...could be cyano
is actually a blue-green algae/bacteria -- we often see it as red or maroon in our tanks, but just as often, it is a greenish color.
Is it like a slimy, almost velvety coating? If yes, then it's likely cyano
Do you think my water quality will go through any type of mini cycle while incorporating the new sand into the bacteria bed?
Was it live sand? If not, then no. If yes, then the amount of "die-off" (and subsequent cycling) will be dependent on how long it was out of the water.