I have the same thing. I switched from a 55 gallon to a 120 gallon cube and all the coraline on my rocks started to disappear. I have some starting to appear on my glass now, but very little on the rocks. I'm sure it will come in time. I wonder: Does coraline grow better under a certain spectrum of light? I was lacking in the blue spectrum, but I recently added more blue so I wonder if I will see a increase in coraline growth. Interesting subject, thanks for the post! :)