Thats sand haha! Thats one reason I am selling it! It call out of a tank I just tore down and it really doesn't fit in my new tank. Thats the one spot it does, but the dang sand keeps getting blown on it so I constantly have to blow it off!
Thats corrects. The white on the edges is growth. The white specks are sand. And the white blotches are where I had to leave for a little and the sand layed there!