Spring Pond Algae Invasion

Reader Contribution by Kenneth Rust

This time of year as I talk with pond owners all over the nation, there are a full range of conditions. My friend Mike from Tennessee, referring to Baton Rouge, said, “Yep, I imagine the birds are already a-whistlin’ down there.” And so they are. Just this week, I swam in a pond for the first time to help a friend create spawning habitat for his fish. I also saw my first two snakes. In Louisiana, spring has arrived. Quite a contrast to my Northern friends, who have suffered through the “Polar Vortex,” which seemed like a whole season instead of an event. One thing for sure, temperatures are warming and spring is on the way. Warmer temperatures for pond owners always means algae production. While we welcome spring, it is also the season for the not-so-welcome invasion of algae.

The 3 Types of Pond Algae

Three types…Now these aren’t the only three types of algae, but these are three categories that will likely be important to you and your pond biology.

Green Phytoplankton: This algae is single-cell, free-floating algae. It is most often noticed as a green color to the water. It can range from a just a greenish tinge to pea soup. Green algae is productive and useful in the pond. Assuming you have sunny weather, it is a net producer of oxygen in the water. It is also the basis for the food chain for a bass-bluegill system, and contributes to other food webs as well. While it is a “good” algae, it can overproduce and the population eventually crashes, if the pond is too rich with nutrients. The level of production desired is also a matter of personal preference, depending on your goals for the pond. If you want to use the pond for swimming, typically, you will prefer little algae production of any kind.

Blue-green: This is the “mutant, evil twin” of green phytoplankton. Blue-greens are difficult classification for biologists. Cyanobacteria: Half-algae, half-bacteria. Blue-green algae are a deep green color, although they can vary from green to distinctly blue. Since it forms dense colonies and floats, it looks like someone spilled green paint on the water. The dense floating nature of blue-green algae shades out the green phytoplankton below, which reduces oxygen levels. Blue-green algae are not net producers of oxygen through photosynthesis. They are associated with high nutrient levels in the pond, and produce bad odors, off-flavor in fish, poor oxygen conditions, accelerated sludge accumulations, and they have been associated with toxic reactions in both pets and humans.

Filamentous Algae: Most often called pond scum, pond moss, or more scientifically, “that #%@# stuff that keeps getting on my fishing hook.. There are several species. Some, like Spirogyra, grow in the winter, which is also the name of a really good jazz group, although the group spells its name wrong. Once water warms, spirogyra burns off. The warm weather varieties, like Pithophora, are the most aggravating. Ptihophora begins as mats along the bottom of your pond while temperatures are still cool and you are unaware. Then when warm temperatures arrive, the bubbly mats float to the surface and drive you crazy while you enjoy your pond.

Algae Control

A common scenario : A pond owner has a flare-up of algae in the pond. The pond owner goes to the local feed store or farmer’s cooperative to inquire about how to handle it. The store salesperson, or Cliff Clavin, the eavesdropping customer, with limited knowledge but in and effort to have some solution, directs the pond owner to use copper sulfate because it is cheap, and they heard about someone using it that one time. Many farm stores carry copper sulfate because they have very limited knowledge, want to provide some solution, it’s inexpensive, and they heard of someone using it once. Satisfied with the consultation and small investment, the pond owner returns home. After opening  the container, he gazes, hypnotized,  at the blue crystals hoping they will magically tell him the dosage to use, since he doesn’t actually know the volume of water in his pond and reading a label is frustrating. Using the scientific method of selecting the largest clump of crystals that breaks off first, he proceeds to use Cliff’s advice of putting the blue crystals in a leg of panty hose and dragging it around behind the boat while it dissolves. Copper sulfate is a very effective algaecide, bactericide, and fish poison when used incorrectly —without regard to water chemistry or volume. Unfortunately, the all-too-common character in this story wakes up the next morning to a pond full of dead fish.

Approach Algae Control … Organically

Physical removal is an option for filamentous algae since you can grab it. A lake rake is a wide aluminum rake with a float across the top. You throw it out with a rope attached and pull it in to shore. This sounds easier than it is since it has a large volume of water and can be difficult to handle., Dragging a chain across the bottom of the pond to disturb the formation of filamentous algae along the bottom also can be used effectively. 

Dye reduces the amount of sunlight penetrating the water to stimulate algae growth.  Shading helps reduce all types of algae. Blue or black dye is available in liquid or packets of water-soluble dry powder.  Blue dye is associated sometimes with the “Tidy Bowl”-blue of miniature golf course ponds. It can be used in a limited fashion to make your pond more attractive and to help reduce algae growth. Dyes are safe for pond inhabitants as well as other visiting wildlife, including humans.

Beneficial bacteria treatments add a high concentration of cultured, beneficial bacteria to your pond. The objective is to create a bacterially-dominated ecosystem, instead of an algae-dominated system.  The bacteria don’t kill algae, they out-compete them — making nutrients unavailable for algae. These bacteria, especially in the presence of adequate oxygen, can be effective and arrest and reverse sludge buildup in your pond. These beneficial bacteria do not cause disease, and are safe for pets, irrigation, livestock, and people.. The secret to predictability with bacterial treatments is consistent, scheduled treatments at the full, recommended dose. I know this means reading a label and possibly doing math, but it really is important this time. Choose a  dry products because they are more concentrated and cost less to ship.

Barley straw has had much acclaim for reducing algae growth.  Its use began as a technique to control algae in open wells in Scotland. Lignin coats the outside of the straw, and is a hard waxy material. When submerged in water and exposed to sunlight, it breaks down, and one of the byproducts is peroxide. Peroxide is algaecidal. The bad news is that this effect is fairly localized unless water is flowing past.. The straw has to be replaced monthly and the old straw removed. This can be a lot of work for an inconsistent result.  Several products, including flakes and extract, give more consistency, with less bulk handling of straw. Peroxide products are available in a predictable, concentrated form for algae control. The good news is that peroxide has an organic label. Green Clean peroxide is available in liquid or granular and is OMRI certified. I have used this product with success. 

Ultraviolet (UV)sterilizers are used for water gardens and koi ponds. This is sound technology and works well at clearing green water from ponds. A filter exposes water  to ultraviolet light. When sized correctly for water volume and flow rate, a UV filter will kill 99.99 percent of algae, virus, bacteria, protozoas, and fungus. A UV filter in the plumbing and kills only the free-floating algae. In water gardens, this is cost-effective and doesn’t use much energy. Vegetable farms use UV technology  to  reduce coliform counts in vegetable irrigation.

Buffered alum binds phosphorus and also drops out small particles like clay in the water. Phosphorus is one of algae’s main nutrients, and vascular plants also need it. Alum, or aluminum sulfate, binds phosphorus into a salt crystal and takes it out of availability for algae. When aluminum sulfate goes into solution, however, it makes an acidic reaction and shift in pH. Your fish won’t appreciate that shift much, and will express disapproval by gulping at the surface in a stressful manner, and possibly floating upside down in your pond (this isn’t so you can scratch their belly). Fortunately buffered alum products on the market prevent this reaction. I have used this product in both water gardens and natural ponds with great success and without harming fish. As a bonus, this product will help to clear your water of small organic particles, clay particles, and even tannins that cause tea color.

“Phytoremediation” with plants along an edge or in bog filters, work for water gardens, natural ponds, stormwater ponds, and even septic and industrial waste treatment. Running the water past the roots of plants allows them to take up nutrients and even pollutants. Coupled with correct sizing, some proven design for the construction, and a commitment to some maintenance, the results can be incredible. 

Next time I will visit with you about a fantastic addition to the edge of your pond or water garden, Louisiana irises. 

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