i am not shur what this is but i believe that it is green hair algae
iv been reading lots of stuff on how to get rid of it but their r so many choices and lots of people say half don't work.
Boy, that's some thick stuff! What size tank do you have, what do you have in it, how long are your lights on for and what kind of water flow do you have, could you be overfeeding? All of these might have something to do with that much algae. You could get some emerald crabs and/or a lawnmower blenny, but I think you need to get control of the reason why this is happening first, IMO.
Need a good clean up crew, one on this site will help you, STARVE the hair algae, by removing nitrates and phosphate, KEEP UP with your water changes..
You can also take out the rock and scrub it with a toothbrush to clean it up. Then, as has been said, you should invest in some nitrate and phosphate reducing solutions.