Aquatic dyes are commonly used in lakes and ponds to retard (slow) weed and algae growth and are available in a variety of colors. All plants need sunlight to grow. By reducing the amount of light penetration into the water, the dyes effectively reduce weed growth no matter which color you choose. It should be pointed out that dyes will not stop weed growth, but used consistently, they will greatly reduce it. Lake and pond dyes may also used to improve the appearance of your water.
Pond dye works best in ponds with good water clarity and only retard weeds and algae that are growing at the bottom of the pond, a good rule of thumb is that pond dyes will not affect any weeds and algae that are already in existence, only new growth. Pond dye can be used year round. Normal treatments generally last 1 - 3 months in contained ponds or lakes. How long the dye will last for you will depend on how much flow you have going in and out of the pond.