"What's it all about...Algae? 
Is it just for photosynthesis you live?"

The most common nemesis of every backyard pond is algae. This tiny plant can cause the water to look like milk or it can create long, stringy masses to clog the ponds. It can detract from the beautiful aquatic plants and interfere with the life cycle of fish.

Most pond owners spend a lot of time and effort preventing or eliminating algae. The key to dealing with algae is to remember that it is, after all, a plant. It has the same requirements as all other green plants...namely:

Photosynthesis - All green plants produce their own food through a process called photosynthesis (Plant Science 100). Algae needs light, nutrients, warmth, water and chlorophyll to complete the process. It needs a minimum amount of all of these factors and if one is missing, the process shuts down. To minimize algae in the pond, we need to reduce the levels of several factors.

Light - Without light...no photosynthesis...no algae. Unfortunately, it also means no water lilies or warmth in the water. So, we are really left with the option of minimizing the amount of light that penetrates into the pond.

Floating plants and the leaves of water lilies will help to cover the surface of the pond. Shading about 70 to 80% of the surface area will help to reduce the amount of algae. The remaining open water will be plenty to allow for viewing fish as they swim around in the pond.

In extreme cases or when no fish are in the pond, dyes may be used to color the water. These will make the water appear black or blue and will filter out the sunlight.

Nutrients - Again, all plants need nutrient elements to provide the building blocks for sugars and carbohydrates created during photosynthesis. Nitrogen and phosphorus are tops on the list of nutrients required for algae growth and bloom.

Guess where a lot of these nutrients originate. Those cute little fish swimming around in the pond have a nasty habit of using it for their bathroom. They release nutrient rich waste into the mix which is wonderful fertilizer for the algae.

A second source is the waste from other aquatic plants. As leaves die and start to rot, they too release nutrients into the water. Leaves from nearby trees and other debris that falls into the pond add to the load. It is all part of Nature's way of recycling.

Ironically, a third source is the pond owner himself or herself. We add to the problem in a couple of ways. One is that we are told to routinely press little fertilizer tabs into our aquatic plant pots. As with most home fertilizer routines, most people overdo it. They fertilize their aquatic plants way too much and a lot of the nutrient value ends up floating in the pond, available for the algae.

Another way that we people contribute is by feeding our fish way too much. Our fish become pets and, as with our dogs and cats, we enjoy making them happy. We like to watch them come to the surface and beg us for food so we do it a lot. The fish grow fat and sassy but a larger fish also produces more waste. More food in equals more waste (i.e. nutrients) out. 

Filters - One of the most important aspects of maintaining a healthy, attractive backyard pond is filtration. Fish and decomposing plant material are constantly adding nutrients and chemical waste products into the water. If these build up in the water, it can cause problems for the fish and will contribute to the algae problem. Filters help bring the pond back into natural balance which will tend to keep the fish, plants and you happy.

Algaecides - Of course there are chemicals out there that are supposed to make algae control quick and easy. Some of these are meant to just kill the algae while others cause a chemical reaction which pulls masses of algae together and drops it to the bottom of the pond.

Both types seem to work but they offer only temporary respite from the problem. What happens when you kill the algae? Does it magically disappear? No, it drops to the bottom of the pond and begins to decompose. When it breaks down, it too releases its nutrients and, eventually, algae will return. Then, you will have to treat again...and again...and again.

Algae control products are available, however, they should be considered as a temporary solution to the problem. As long as there is are nutrients and light present, the algae will return to the pond. If you have a serious algae growth, the long-term answer is to reduce the number of fish, increase the filtration, decrease the light or otherwise restore the balance of the pond.

 

A "non-chemical" approach to algae control which is gaining popularity is floating a bundle of barley straw in the pond. The suppression effect on the algae is due to the allelopathic effect. Certain plants produce chemicals that are natural "herbicides" to other plants thus giving one plant an advantage over another. The classic example of this phenomenon is the impact that the roots of black walnut trees have on nearby plants such as tomatoes. Someone discovered that barley straw has this type of effect on algae in a pond. Still, just like the chemicals, this is a short-term control measure. Balance is what nature seeks!