Could be a few reasons for a lack of coraline algae. First, make sure you have sufficient lighting and calcium levels. I've got 110W PC and 7100 blue actinic on my 46G, my calcium ranges between 420 and 480 (usually at 450) and I am loaded with purple and red corraline. Also, if you have diatoms, you can eliminate them by removing silicates from your water. I use phosguard in my emporer filter to keep my phosphates and silicates very low. Diatoms are tiny organisms whose structure is comprised of silicates: no silicates = no diatoms.
And definately get a clean up crew, they'll help you out by keeping the bad algae down and leaving the coraline alone.