Its a big topic on lots of the web based forums on getting coraline to
grow by the scrape / seed method. Theory has it that if you scrape the
coraline off the glass etc, and collect it, and place it in another
tank it spawns new coraline growth, or the mere process of using a
tooth brush to scrub coraline promotes it to spawn more.......I have a
tank (10 gal) I use for aQT, but as of late I have been keeping sand
in it. The sand wsa removed from an established tank I reduced the
sand be in, to 1" or so deep, and I did not want that sand to die off
on me. No live rock but there is a heap of that sand in there that has
pink scrapings from coraline in and there is not the first hint of
coraline growing anywhere in that tank like powerhead , filter intake
tubes / overflow weir etc......nowhere..Its been that way perhaps 8
months.......

Do you have light on it?