I use 1) Gray rubber maid can. 2) Heater. 3) Power head. 4) An air stone. I take the rock and swish it around in old water. Then I scrub it with a brush. I Change some water every 2# weeks, and repeat. Swish and scrub, every time I change water. 3 or 4 months. Now the rock is back in good shape. I do this to kill off algae like bubble and Caulerpa, plus the detritus.