Pure Blue Pond Dye is an all natural tool to limit weed and algae growth in large ponds. This easy, effective and earth friendly product naturally reduces sunlight reaching the lower layers of your pond, by restricting sunlight, you limit the potential for excessive weed and algae growth. One Gallon treats 5 surface acres, or a one acre pond with an average depth of 5 feet, or 1.65 million gallons of water.