Im sorry but I have to ask this. Is the algae your refering to growing on top of the rocks or on the glass? I honestly dont see anything thats white on the back glass. I do see some round areas where the green algae is not on the back but the color does not appear white.
The white on the top of the rocks could be coraline algae that is bleached out. Possibly due to an increase in light from what it was previously growing in.
__________________ Remember dont tap the glass, your fish will think you're an idiot-Anonymous mother
This looks like green film algae from the glass wall of the tank? It appears something has either been nibbling it (no animal trail though?) or by the symetrical shapes, it's coralline trying to break through. Is the newer algae very hard or easily removed with your finger?