I generally use a whole bottle poured across my waterfall because that's where the algae grows the worst. The bottles I get have a hole in the lid so you can squirt it on an area. I use this to squirt directly into the middle of the worst patches around my pond. After about 5 minutes you will see the algae bubbling and clumps floating to the surface. I don't think I would treat more often than once every week or two if you have fish, and I don't use it near the invertebrates (like snails).