Currently have 55 gallon fuge, 3in live sand and 50 pounds of rock but my nitrates don't come down from 40 ppm do to tap water ,and there's brown stuff on top of the sand bed that looks like wastes.
See/read about/buy it from this site:
https://www.saltwaterfish.com/Chaeto_p_2010.html
Two weeks after installing my HOB fuge and adding chaeto, my nitrates dropped to undetectable levels.