I tried shaking dark gravel to clean. I changed murky water in a PET bottle. The photos shows the phases. Shaking times were 1h25mim, 1h25min, nearly 3h. It smelled algae strong at phase 1, when I opened a cap of the bottle. I suppose the gravel deposited algae or somthing for 10 years.
Gravel did not seem green before shakes at all. The gravel was dry for winter. Plants like algae are tough to dry up, I think. The shaker is effective to clean gravel. Motion picture shows how the polisher works and gravel is washed.