Because pond scum and algae are living organisms, they are rich sources of nitrogen that break down quickly in the compost pile. Using pond scum as fertilizer also incorporates important nutrients, such as potassium and phosphorus, into the compost.
To incorporate pond scum into a compost pile, begin with a 4- to 6-inch layer of carbon-rich (brown) materials such as straw, cardboard, shredded paper or dead leaves. Mix the pond scum with other nitrogen-rich (green) materials such as vegetable scraps, coffee grounds, or fresh grass clippings. Spread about 3 inches of this mixture over the brown layer. spread up to 3 inches of the compost over the soil just before spring planting, then dig or plow it into the soil, or spread the compost evenly over the soil as mulch.
If you however want to reduce algae out of your pond and not use it for your garden, then its important to remember a few things. First: Having beneficial bacteria in your filter does not reduce algae. The bacteria turns ammonia into nitrites and nitrites into nitrates and algae loves to eat nitrates. A filter only helps with algae by capturing waste, and then when you clean your filter, you are removing that waste from you pond. If you don’t clean your filter then it will break down in your filter and produce the nutrients that your algae love to live on. Second, take effective measures to cut down nutrients in or near the pond. You see, algae blooms are basically caused by too much nutrients available to algae. By providing a buffer zone that separates the pond from your garden or lawn, you disallow fertilizers and other food sources to benefit algae. You must also clean your pond regularly to take out any decomposing organic objects that can serve as algae food. Finally, put fish in your pond that will make a meal out of algae. Carps are known to feed on soft algae. With herbivorous fish, you have live anti-algae measures in place that will make sure these microscopic plants cannot bloom out of proportion.