Plant Answers

Algae in Your Pond!

Question: My fish pond is outside and holds 100 gallons of water. Algae is taking it over. How can I control it?

Answer: Excellent question! Algae tends to be one of the biggest challenges that pond owners face. And since there are over 3,000 types of algae, it can be rather intimidating! Whether you have a small pond or a huge pond, sooner or later we all face the challenge of algae.

You didn't explain just what type of algae you have. The two types of algae are floating single-cell algae and filamentous "stringy" algae that attaches itself to objects in the pond. The single-cell algae is what gives us green water. I'll cover both types for you, as the controls are basically the same.

One of the biggest causes of algae is too much sunlight entering your pond's water. The sunlight creates the algae. If you have a pond with plants and fish, you can usually control this by having 75% of your pond's surface covered with water lily leaves. The leaves cover the surface, thus blocking the sun's rays from entering the water. Algae needs the sunlight to grow.

Winter tends to be a challenging time for algae control. Due to the plants being dormant, the sun gets full access to the pond. Even though the water temperature is lower, a "winter algae" can easily take control of your pond.

Another thing that works hand-in-hand with the 75% rule is to have submersible "oxygenating" plants. Two common such plants would be Anacharis and Cabomba. (Thankfully, 75% of the pond's bottom does NOT have to have oxygenating plants!) No more than one or two pots would suffice for a pond
your size. Actually, I'd just put one pot in there as it will grow like a weed and you'll soon be pulling it out.

Another common source of algae is too much nutrients in the water. This is the result of too many fish and/or inadequate filtration. You can manage without filtration if you have a very few fish and adequate plants.

One of the most common situations among pond owners is having a pond that is overstocked with fish. If you want more fish than a pond should have, then you need to make up for it by having at least double the filtration for that size pond. There is NO such thing as too much filtration.

There are also products on the market that you can use to help control algae. A very common one is AlgaeFix that is made by Aquarium Pharmaceuticals. You can even buy it at some pet stores. An organic method is the use of barley straw products. (NOTE: Barley straw does not always work
though. It seems that a big factor in its success is the hardness of the water.) Be careful though, as the dying algae can create a severe loss of oxygen that could possibly result in loss of fish life.

One cure of the floating single-cell algae that works 100% of the time is the use of ultraviolet lights. This is a special unit that pond water slowly flows through UV light and the algae cells get killed by the UV rays. If you have plants in your pond though, the use of a UV light is NOT necessary. I have talked to many people over the years that were ready to start pouring chemicals in their ponds or to install expensive UV light systems to get clear water. Their algae problems cleared up simply by adding plants. Mother Nature is the best algae control there it!

I hope that this helps you in your quest to control your algae. Please feel free to contact me with any further questions. Duane Eaton at www.thepondplanner.com (San Antonio, Texas)