Filamentous Algae Control Methods And Best Management Practices
Updated: Aug 9
Hello fellow Pondologists, and welcome to the very first installment of “Pond Weed Problems”! In this series, we will explore how to take control of aquatic weeds and pests in your pond.
First, let's establish a basic definition: a weed is simply a plant growing where it is not wanted. Just like pulling a patch of crabgrass out of your pristine Kentucky Bluegrass lawn, if there is a plant in your pond you want to get rid of, it's a weed—don't let anyone tell you otherwise!
Note: Always make sure to check with your local laws and regulations before using any recommended treatment options.
In today’s entry, we are tackling a notoriously frustrating pond pest: Filamentous ALGAE Control Methods.
The Ecology of Filamentous Algae: Know Your Enemy
Filamentous algae, often referred to as "moss," is one of the most frequent challenges for pond owners. Effective management requires an understanding of its biology and environment, rather than just immediately reaching for chemicals.
Identifying the Culprit
Before treating, you must properly identify the algae. Filamentous algae grows in long, hair-like strands or threads. These intertwine to form dense mats. They typically begin growing on the pond bottom or attached to submerged objects. As they mature and trap gases from photosynthesis, these mats float to the surface.
It is critical to distinguish filamentous algae from other aquatic growths:
● Planktonic Algae: These are microscopic, single-celled organisms. They remain suspended in the water column, giving your pond a greenish tint.
● Chara: While often mistaken for a submerged plant, Chara is actually a macroalgae. Unlike the soft, slimy feel of filamentous algae, Chara has a gritty, bristly texture. It also emits a musky odor when crushed.
The True Drivers: Nutrients and Sunlight
Like plants, filamentous algae needs two things: sunlight and nutrients. An explosive algae bloom is almost always the direct result of too many nutrients (primarily phosphorus and nitrogen) in the water. Because algae absorb nutrients directly from the water column, their growth is directly tied to your pond's nutrient load.
Where do these excess nutrients come from?
● Runoff from fertilized lawns and agricultural fields.
● Waste from livestock or pets.
● Decaying organic matter like leaves and grass clippings.
● The deliberate feeding of fish or waterfowl.
If your pond has a high nutrient load, it is essentially a pre-fertilized garden just waiting for warm temperatures and sunlight to spark a bloom. A severe bloom is a symptom of nutrient pollution. If you only use chemical treatments without addressing the root cause, you will be locked into a costly, perpetual cycle of treatment and regrowth.
The Crucial Step: Pre-Treatment Assessment
An Integrated Pest Management (IPM) strategy views chemical algaecides as a reactive, temporary tool to knock back an infestation so you can implement long-term preventative measures. If you decide chemical intervention is warranted, you must perform a pre-treatment assessment. The vast majority of fish kills are caused by user error during this phase.
Step 1: Calculate Accurate Pond Volume
Chemical labels provide dosage rates based on water volume. Overestimating will lead to a toxic overdose for your fish, while underestimating will waste product and fail to control the algae. Ponds are measured in acre-feet.
● The Formula: Acre-Feet = Surface Acres X Average Depth (ft).
● Example: A 4-acre pond with an average depth of 5 feet contains 20 acre-feet of volume.
Step 2: Test Water Chemistry
Testing your water's Total Alkalinity is absolutely mandatory if you are considering copper-based products. Total Alkalinity measures the water's capacity to neutralize acids, expressed in parts per million (ppm) of calcium carbonate. Alkalinity is not the same as pH or water hardness. You can get a test through local extension services or purchase a comprehensive kit from Pondology101.com.
A Comparative Analysis of Chemical Algaecides For Filamentous Algae Control
When intervention is necessary, pond owners generally choose between copper-based compounds, peroxide-based oxidizers, or specific aquatic herbicides.
1. Copper-Based Algaecides (The Traditional Workhorse)
Copper disrupts essential cellular processes in algae, causing cell membranes to rupture. It is effective and relatively inexpensive, but requires precision.
● Copper Sulfate: This is the most widely available and cheapest form. However, its safety is entirely dependent on your Total Alkalinity.
○ Low Alkalinity (< 40-50 ppm): Copper exists in a highly soluble, ionic form that is exceptionally toxic to fish. Never use copper treatments in these conditions.
○ High Alkalinity (> 250-300 ppm): Carbonate ions bind to the copper, causing it to precipitate into the sediment where it becomes completely ineffective against algae.
● Chelated Copper Formulations: To solve the precipitation problem, these products bind copper ions to an organic molecule (a "chelating agent"). This protective shell keeps the product suspended and active in the water longer. It requires lower concentrations of copper, making it safer for fish and more reliable across various water conditions. Granular forms are excellent for targeting bottom-growing algae.
2. Peroxide-Based Algaecides (The Rapid Oxidizer)
For a more environmentally benign approach, look to products containing sodium carbonate peroxyhydrate (SCP).
● How it Works: When these granules hit the water, they break down into soda ash and hydrogen peroxide. The hydrogen peroxide aggressively oxidizes and destroys algae cell membranes on contact.
● The Benefits: The reaction is visibly apparent, often causing the algae to fizz, bubble, discolor, and die within minutes. Afterward, the peroxide quickly decomposes into harmless water and oxygen, leaving no chemical residue behind. There are no
waiting periods for swimming, fishing, or irrigation.
WARNING: Protecting Sensitive Species Copper sulfate and chelated copper products should never be used in ponds containing koi, ornamental goldfish, or trout. These species are exceptionally sensitive and can be killed by standard copper concentrations. Furthermore, copper is a heavy metal that bioaccumulates in fish tissue over time, leading to compromised immune function and shortened lifespans. If you have sensitive fish, a peroxide-based algaecide is your only responsible option.
3. Other Relevant Herbicides
● Diquat: A broad-spectrum contact herbicide. Limitation: It binds tightly to suspended sediment, making it completely ineffective in muddy or turbid water.
● Endothall (Amine Salt): A potent contact herbicide and algaecide. Limitation: It is highly toxic to fish at concentrations above 0.3 ppm and can severely irritate the applicator's skin and eyes. This is usually best left to licensed professionals.
● Flumioxazin: Effective against tough algae like Pithophora and Cladophora. Limitation: It is extremely sensitive to pH and degrades in minutes if the pH is above 7.5. It must be applied in the early morning when the pond's pH is naturally at its lowest.
Field Guide to Algaecide Application
Once you have assessed your pond and chosen your product, application requires tactical precision.
Applying Copper
● The Dosage Calculation: Do not guess! Use this formula: Pounds of Copper Sulfate = Acre-feet X (Total Alkalinity[ppm] / 100) X 2.72.
● Method: The best method is to dissolve the crystals completely in a bucket of water and spray the solution evenly over the target area. This maximizes contact and prevents toxic "hot spots" on the pond bottom.
● Equipment: Because copper is corrosive, only use plastic or stainless steel equipment, and rinse thoroughly after use.
Applying Peroxide (SCP)
● The Dosage Calculation: There is no universal formula; rely on the product label's range based on the visual density of the algal growth.
● Method: Broadcast the granules evenly over the surface. For best results, use a rake or a high-pressure hose to break up dense mats right before application so the granules can penetrate.
Optimal Environmental Conditions
● Temperature: Apply when algae are actively growing, which requires water temperatures of at least 50°F (consistently above 60°F is recommended by most labels).
● Time of Day: Early morning is the best time to apply. The pH is lowest (critical for Flumioxazin), sunlight enhances peroxide products, and it avoids compounding the natural drop in dissolved oxygen that ponds experience overnight, creating a safety buffer for fish.
Alternative & Complementary Management Practices
To eventually reduce your reliance on chemical interventions, you must create an environment that is inhospitable to algae.
● Aeration: Installing a bottom-diffused aeration system is one of the best investments you can make. It prevents stagnation, increases dissolved oxygen for fish and beneficial bacteria, and helps chemically bind phosphorus into the sediment. Surface aeration is also an effective tool in shallower ponds. It increases oxygen, turbulence, and helps expedite biological processes and decomposition.
● Nutrient Mitigation: Legacy phosphorus builds up in pond sediment, especially in ponds older than 15 years. Applying a phosphorus binding agent can reset your pond's phosphorus load and drastically reduce algae growth.
● Sunlight Limitation: Non-toxic aquatic dyes (blue or black) inhibit the photosynthesis algae needs to grow. Dyes must be applied in early spring before algae is established, and they are only effective in water deeper than two feet.
● Physical Removal: Skimming or raking algae out of the pond offers immediate control. Be sure to dispose of the algae far from the edge so the nutrients don't wash right back in as it decomposes. Be warned: this is highly labor-intensive and time-consuming!
A Note on Barley Straw
Barley straw is a popular, non-chemical algistat. It does not kill existing algae, but as it decomposes, it releases compounds (possibly hydrogen peroxide) that are believed to inhibit new growth.
To use it, 2 to 5 bales (approx. 225 pounds) per surface acre must be broken apart into mesh bags and anchored near good circulation (like an aerator) in the early spring. However, research on its effectiveness is mixed, its action is slow, and ultimately, it adds more decomposing nutrients directly back into your pond, which compounds the root problem.
The Final Word
A multifaceted, preventative approach is your key to lasting success. By addressing nutrient pollution and cultivating a balanced ecosystem, you can ensure a healthier, clearer, and more stable pond for years to come!
If you're more of a visual learner (like myself) make sure to check out the video version of this blog post by clicking on the link below!
Comments