Normal, no. Possibly Cyanobacteria. Siphon out and increase flow to that area and turn your lights off while the tank is cycling. It should go away in a couple days.
Coralline algae? In 3 days and on the sand bed?
First lets determine if it is in fact Cyanobacteria ok. Take a turkey baster and lightly blow on the area, and or try sucking it up. If it blows off and your able to remove it, then it is in fact cyano.
For better reference just Google Cyanobacteria for picture ID.
When I was cycling my tank it appeared due to the lights being on and seemed to appear in locations that werent getting much flow. I ended up turning the lights off and sucked it out and after a day it was gone as far as keeping it from returning my guess would be to ensure you have a good flow.
Had it in my dads 190L tank i put together for him he now runs a fluval 406 external 1500 lph and internal filter 1000 lph and a 3500 LPH powerhead no sign of it anywhere and I put a Goby and a blenny in they characters to watch.