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Algae, under certain conditions, can quickly overtake a pond, turning the water green, reducing oxygen levels, and impacting the health of fish and plants. While some algae are natural and beneficial, excess algae needs to be managed. In this guide, we’ll cover various ways to prevent/control algae, keep it from spreading, and tackle specific types and forms for a clear, healthy pond environment.
Algae play a role in the pond ecosystem by providing oxygen, serving as a food source, and absorbing excess nutrients. However, when algae grow out of control, they create imbalances. Too much algae can reduce oxygen, cloud water, and even release toxins that harm fish.
In a small ecosystem like backyard water gardens and small to medium-sized landscape ponds, algae can easily over-burden available resources and slew those ecosystems out of balance. This is generally bad and can lead to some serious, recurring problems or your pond.
Clear water that’s enjoyable to look at
Healthier environment for fish and aquatic plants
Reduced risk of harmful algae blooms
Increased biodiversity in the macrobiotic community
Controlling algae in ponds requires a balanced approach. Here are some effective methods for backyard koi ponds/water gardens:
Reduce Sunlight Exposure: Algae need sunlight to grow, so shading part of the pond can help limit its growth. Floating plants, such as water lilies, provide natural shade and help prevent algae from spreading.
Control Nutrients: Excess nutrients from fish waste, fertilizer runoff, or decaying plants fuel algae growth. By minimizing these inputs, you can limit algae. Installing a pond filter can also help remove organic waste before it feeds algae.
Pond Cleanouts are also helpful in this scenario. Annual/semi-annual cleanouts are necessary for most garden ponds.
If you need guidance on how to perform a pond cleanout, please read the below blog entry…
Spring Pond Cleanout: Essential for Aesthetics and Fish Health
Add Beneficial Bacteria: Pond-safe treatments containing beneficial bacteria break down organic waste, reducing the nutrients algae rely on. This natural method can significantly reduce algae without chemicals. A good bacteria product will directly compete with alga for resources.
Tip: Installing a pond aerator improves circulation and reduces stagnant areas where algae thrive. For koi ponds that are large enough (i.e.greater than 20ft x 20ft), a small fountain performs fantastically as an aerator and aesthetic backyard enhancement.
If algae have already taken over, the following steps can help you clear it out:
Manual Removal: Start by removing as much algae as possible with a pond skimmer or rake. This method is especially effective for larger floating mats of algae. It’s a workout for the shoulders, but it will save you time in the long run.
Water Changes: Partial water changes can help dilute nutrients and remove some algae, especially in small ponds. Always use dechlorinated water if added from a tap.
Water Treatments: Add treatments weekly to maintain a good bacteria population.
Barley Extract is a great natural algae preventer for small water bodies – safe for Koi too!
Use Algaecides Sparingly: In severe cases, pond-safe algaecides can help. However, use them sparingly to avoid harming fish or plants. Look for algaecide options designed for safe pond use, especially if you are keeping koi, catfish, or trout.
I recommend contacting me (or another qualified biologist) so that I may recommend a specific product and dosage for your situation.
Quick Fact: A study found that ponds with regular water changes and circulation systems had 30% less algae than non-aerated ponds.
String algae, also known as filamentous algae, are long, green strands or mats that float on the surface or attach to pond walls. They’re unsightly and can reduce oxygen levels, harming fish.
Manual Removal: Use a weed rake to pull out string algae from the pond’s surface. Removing it before it spreads reduces the chance of regrowth.
Limit Sunlight: String algae grow quickly in full sunlight, so shading parts of your pond can slow their growth. Adding floating plants or a pond canopy helps reduce sunlight exposure.
Introduce Beneficial Bacteria: Some water treatments introduce bacteria that consume nutrients string algae need. These treatments work over time, providing sustainable algae control.
For more detailed strategies on managing string algae, our guide on string algae control offers effective, eco-friendly solutions.
Preventing string algae involves combining preventive measures with regular maintenance. Here are some additional tips:
Circulate the Water: Using a pond pump to keep water moving makes it harder for string algae to form dense mats. Circulation also improves oxygen levels, benefiting fish and plants.
Add Barley Straw Extract: Barley straw releases natural compounds as it decomposes, which prevent algae growth. I recommend the liquid extract over the bales, It’s more concentrated AND effective as an algae deterrent.
Regular Pond Cleaning: Removing debris and organic waste before it decomposes reduces the nutrients string algae rely on. A pond skimmer can make regular maintenance easier.
For pond owners who prefer to avoid chemicals, natural methods for killing algae are effective and eco-friendly:
UV Clarifiers: UV lights kill algae cells by disrupting their DNA, reducing free-floating algae in ponds. While it won’t prevent all algae types, it’s very effective for clearing up green, cloudy water.
Add Aquatic Plants: Aquatic plants like Arrowhead, Blue Flag Iris, and water lilies absorb nutrients that algae need to grow. Adding a variety of plants not only beautifies the pond but also reduces algae.
A pond study in the UK found that ponds with at least 30% plant cover had significantly lower algae levels compared to bare ponds.
PLANTS, PLANTS, PLANTS, PLANTS, PLANTS, PLANTS, PLANTS, PLANTS, PLANTS, as soon as you think you’ve planted enough plants, go get some more. They are the hardest-working organisms in the pond - and the biggest bang for your ecological dollar.
Q: Can I remove all algae from my pond?
A: Complete removal isn’t necessary or practical, as some algae are beneficial. The goal is to control algae so it doesn’t affect pond health or appearance.
Q: Is it safe to use algaecides in a fish pond?
A: Yes, but only use algaecides labeled safe for ponds with fish (or a particular species of fish) and follow instructions closely. Overuse can harm fish or plants.
Q: How often should I remove algae from my pond?
A: Regular monitoring and occasional removal (every few weeks) are usually sufficient. Removing excess algae before it spreads is the best approach. Weekly pond maintenance is almost always necessary.
Regular Maintenance: Cleaning and removing debris regularly keeps nutrients low, reducing algae growth.
Use Preventative Water Treatments: Eco-friendly water treatments add beneficial bacteria that consume nutrients before algae can.
Seasonal Checks: Algae often bloom in warmer months. Adding shade and performing water changes in spring and summer can prevent algae from taking over.
