Well you could try dosing iron in order give the chaeto a kick in the butt so it will start growing well. You'd want to be real conservative on that though or you'll kick off a heck of an algae bloom.

Here's an article on iron in a reef tank...
http://www.advancedaquarist.com/issues/aug2002/chem.htm

Just skip down to the useful info unless you find chemistry formulas interesting :zzz .