What I do when I want rock to be clean and free of pests algaes or stuff like button polyps, I do a bleach bath.
Usually one overnight soak with 2 cups of bleach per 5 gallons of freshwater ( tap water).
That will usually dissolve most organic matter and turn the rock mostly white.
Sometimes a second round is needed. But not very often.
What I do for my own peace of mind is, after the bleach bath, rinse all the rock and then do a soak in a strong dechlorinator solution, such as Prime.
If you don't want to spend the money on Prime or another product, just leave the rock out to dry for a couple days.
I also will do a muratic acid bath. 1 cup per 5 gallons of water. Follow the directions on the acid container. Use rubber gloves and eye protection and do it outside.
This is suppose to help remove phosphate that has soaked into the rock.
