I just got a 38 gallon and bought a load of branch rock with tons of coraline already on it. It's hard to tell in your picture if that is, or is not, coraline. My coraline is a deep purple and covers the entire branch rock I purchased (at a price I might add)
I use a product called, "Purple Up" that has begun to create more pockets of coraline on my LR that didn't already have it on there. The most important part of this product is that it is based on the fact coraline is already growing in the tank. I would try to find a nice small rock from your LFS that they can idenify as having coraline on it. Then, just add PURPLE UP every day and you will start to see coraline beggining to grow.
Hope this helps!