Hi Lindsay - first of - BEEN A WHILE!?!?!? How are you doing!?!?!?
Secondly - when do we see updated pics of your tank again?
Thirdly - I think that the caulerpa WILL die off first, because the nitrates in your sump is far less than it would be in your tank.
Another thing - the locations where you are seeing GHA grow, is MOST likely due to detritus that's hidden inside your live rock, and possibly, sand bed....
Do yourself a favour - where the GHA is growing - take a loose power-head, and blow a strong stream of water on this location - if you see "dust" start going into the water colum - then you know - it is like it....