Ken,
I don't understand, you have an overflow, so I presume you have a sump too, why don't you hide the skimmer in the sump?
For Coraline to grow, you also need to dose some calcium, (and seed it with some LR's covered with coraline too). You need a calcium test kit, and make sure calcium level is between 380-420. Coraline will grow everywhere even in the low light area too.
You will also need to test alkalinity too.