Not long ago I had a huge problem. I found my phosphate levels very high and used a sponge in my magnum h.o.t. Also after talking to other freinds, the consensus seems to be keeping high levels of calcium to promote healthy growth of coraline algae.I am also starting to use another product called coral-vital that also promotes coraline. After seeing the results in my freinds tank,i am confident this is the way to go.