I have green algae on my pondless waterfall rock. Since it is not stringy, I assume it is regular algae and not string algae. I have poured an algecide in but it seems to not clean it off the rock or prevent the green algae from being on the rock. Also, how do I figure the gallons of warter in my pondless waterfall?

Using an algaecide like Oxi-Clean or EcoBlast directly on the rocks will clean up the rocks. Installing an IonGen will help with the green algae on the rocks also. If you do not physically remove the algae, the algaecide will kill it and flush down into the basin, where in a few weeks it will come back. Using a combination of Oxi-Clean and a liquid algaecide like Algaway twice a month usually will keep the waterfall clean. Also, remember that the basin of a pondless should be flushed out in the spring every other year. But to save all the expense and work in doing that, have an IonGen installed is the best option.