Hi there,\nI've installed and maintained several ponds/water features, over the years. Presently, I'm dealing with a pond that has a clarity issue. I can handle that. My question is the algae on the gravel at the bottom of the pond seems to be bothering the owner. A vacuum won't work, without sucking up the gravel. Any other suggestions as to how to rid the pond of this, short of draining and cleaning?