take the rockwork out and place them in a bucket with the water change water, drain the tank fully and scoop sand into a bucket and rinse out with a water hose until the water is clear (this will take some work) once clear rinsed, rinse again in RODI water and place back in the tank. as for the rocks you can take one rock at a time and place it on a towel, use a steak knife to scrape out the roots of the algae and add a drop of hydrogen peroxide to kill off the roots. I would limit the working time frame of scraping on the rocks to about 10 min before putting it back in the bucket of water. place back in the tank and refill with fresh saltwater with the correct salinity and temp.