The pond boss PRO Block Bacteria is a blend of live bacteria and enzymes specifically designed to improve water quality by reducing unwanted organic matter. It is recommended for large ponds and lakes. Leaves, grass clippings, dead or dying plants, excess food and other organic material build at the bottom of the pond in what is known as the "sludge" layer of the pond. The sludge layer is most often responsible for foul odors and low oxygen levels. The regular use of pond boss PRO Block Bacteria will degrade unwanted organic debris accumulation and improve the overall health of the pond while clearing the water column of unwanted organic material. One 5 lb. block can treat up to 5 acre ft. of water and one treatment can last up to 60 days, depending on water conditions. This product is designed to work in combination with our pond boss PRO Water Clarifiers (Item No.CWCPR10 and Item No.CWCPR128).