[billdogg]

I can't tell from the picture, but your description sounds a lot like common bubble algae (valonia sp). IME, nothing eats it. Emerald crabs might pick at it some, but they are hit or miss. Your best option is manual removal. What I do is tie a filter sock around a long piece of vinyl tubing, too the sock/tubing in the sump, and then start a siphon in the tube. Use the end of the tubing to scrape it off as best you can. If the rocks can be removed, scraping it off outside the tank is even better because afterwards, you can pour hydrogen peroxide on the affected areas to kill off the remaining spores. It will take sever attempts to get it, and in the meantime, determine the source of nutrients and reduce them so you are not just feeding the growth of more.

hth