I doesn't appear that you have many corals in the tank, so if that is true, take the rock out and get rid of the stuff. Otherwise, it will grow so fast that it will choke out your corals. I successfully removed majanos that beautifully filled my tank (not knowing they were bad). I used a bucket to scrub the rocks down. I started by scrapping off any that I could see, then cleaning the rest of the cracks and crevices with a toothbrush. After that I rinsed in another bucket. You may have to repeat this process, so don't bother rockscaping yet. If you see any, do it again until they are gone completely. If you do have corals on the rocks, you can still do this process, it is just harder to work around them.

Once you complete the process, you might introduce a file fish in case there are more hiding that you didn't catch. Research the specific kind of file fish to get though first.