i am having the same problem getting coralline to grow, i have a rock that is totally ENCRUSTED in coralline algae (i bought it from my LFS) and ive had it since i started my:
50 gallon reef,
6 month old
2 96watt pc lights
its one of the base pieces for my live rock...should i put it at the top and put a powerhead over it? what does this do btw?