How to Kill Pond Algae

Pond algae is one of the most common aquatic growths. Pond algae needs very little to grow: water, sunlight, and nutrients. All three of these ingredients are found in abundance in every pond. Add these ingredients to a shallow pond or a pond with little surface movement and you have an incubator for algae. The good news is that algae is fickle and as quickly as it appears it can disappear with the proper products and effort.

It would be easy to just recommend using a copper sulfate-based product like Crystal Plex and walk away. This is a great product, we recommend it, and it will kill algae. If this is the only product you choose to use, you will be back in about 2 weeks saying, “why did my pond algae come back?” I would then refer you back to paragraph 1…go ahead and reread it, I’m waiting. Adding the pond algaecide didn’t change the fact that you still have all the ingredients necessary for pond algae to grow. I will save you the time searching…there is no product you can apply one time to your pond to kill algae and have it never return.

Pond Algae Treatment Before and After 

You must change the environment to help prevent and slow down the growth. The easiest way to do this is by using preventative maintenance products like pond dye and pond bacteria. Using these products monthly won’t prevent you from ever getting algae, but it will help slow down the growth and make treating your algae more manageable. Pond dye will help tint the pond and pond bacteria will minimize nutrients. Pond dye and pond bacteria are extremely easy to use, pour both products in around the edge of the pond once a month or when you notice the color in your pond is fading. These products should be applied as soon as the pond thaws.

Using pond dye and pond bacteria will help keep your pond algae close to the shoreline so that it is easier to spray with Crystal Plex. In the spring you should treat your pond with Crystal Plex at the first signs of algae and when water temperatures reach at least 50°F. Monthly applications of a pond algaecide should keep things at bay if you are using your preventative maintenance products correctly. When you get into the warmer months, you may have to treat algae more frequently. For a 1 acre pond with an average depth of 4-6 feet deep, mix 1 gallon of Crystal Plex with a couple gallons of water and spray ½ of your pond’s growth. Wait 5 days and treat the other ½ of the growth with the same dose.

*If you have koi, goldfish, or trout you cannot use any products that contain copper sulfate.

For additional help on killing pond algae check out our blog series on Pond Algae Treatment or contact Sanco Industries.