Let’s Talk about Pond Algae

koi pond string algae

Types of Pond Algae

There are many types of algae. I am no scientist, so let’s just focus on some typical algae that are seen in backyard ponds. I’m going to list the causes, what to know and solutions for each one. 

Pond string algae

String Algae

Black algae waterfall

Black Algae

Microbial Algae

Diatom Algae

Photo of weird algae in waterfall like gel blobs called Nostoc

Gel Balls?

Chara

Beard Algae

String Algae

Might also be referred to as Hair Algae, Filamentous Algae, or Thread Algae. Scientific name is claudophora spirogyra.
String algae, hair algae in ponds, pond algae, koi pond algae
koi pond string algae

Causes:

      • A sudden influx of fresh water from the hose. String algae is a good indication of a leak, especially if there is an autofill putting in water when you don’t realize it. 
      • Excess nutrients in the pond.

Things to know about string algae:

      • String algae is very fibrous.
      • It likes clear water.  It doesn’t mind cold water but it does like the sunshine.  
      • It helps filter the water.
      • It is not harmful to fish unless it impedes their movement.
      • A pressure filter or UV light will not help with String Algae.

Solutions:

    1. Remove as much of it as you can with a long-handled brush or skimmer rake.
    2. Check to see if there is water loss (a leak).
    3. Add more beneficial bacteria.  What is Beneficial Bacteria?  
    4. Add aquatic plants, specifically floating plants to use nutrients, and lilies to shade the water. 
    5. Use an Iongen or Ionizer.   (Follow instructions very carefully!)  I recommend finding the imbalance in the ecosystem and removing the algae by hand rather than using these devices. It’s better to find the source of the problem and fix it, rather than just treat the symptom, which could cause other issues. I am more familiar with the Aquascape IonGen and have used it previously. 
    6. Do not use algaecide unless you have no other choice, and even then, just treat the stream with something like EcoBlast. It is critical that you follow the directions on the EcoBlast! 

Black Algae

So far I don't know other names for it.
water feature black algae

Causes:

      • I am not quite sure.  
      • Algae is generally caused by excess nutrients in the water. 

Things to know about black algae:

      • It is very black and shiny
      • I have not seen it in a pond, it’s always on the waterfall rock area.
      • It can be removed by pressure washing but it seems to come back eventually.
      • It thrives in the well oxygenated area – the waterfall rocks and the edges where there is splashing.
      • This type of algae will not hurt fish or wildlife. Oddly enough, it consumes organic material and other compounds that form, helping to keep pond water healthy. Some people don’t mind the black shiny look.

Solutions:

    1. I am doing some experimenting on this algae to see if I can specifically figure out what causes it and the remedy. The  items below may or may not help. 
    2. Remove as much of it as you can with a long-handled brush or skimmer rake.
    3. Add more beneficial bacteria.  What is Beneficial Bacteria and how often/much should I be adding it?  
    4. Add aquatic plants, specifically floating plants to use nutrients, and lilies to shade the water. 
    5. Do not use algaecide unless you have no other choice, and even then, just treat the stream with something like EcoBlast. It is critical that you follow the directions on the EcoBlast! 

Beard Algae

Might also be referred to as Hair Algae. Scientific name is Oedogonium
Photo of Pond with furry beard algae

This is a closer look at the Beard Algae. The driftwood is covered in it and you can see it adhering to the rocks as well. It looks blurry. Towards the top and center of this picture, you can see it is getting a little longer. This is still beard algae!

Causes:

    • Not enough aquatic plants.
    • Low CO2 in the pond. 
    • Not enough sunlight.
    • Not enough circulation.
    • Too many fish. 

Things to know about beard algae:

    • It is often mistaken for String Algae.  The difference is that it looks like fluffy tufts of green. It can make longer strings but is less stringy than string algae and may fall apart more easily when you grab it. (click HERE to read from another source about String or hair algae) 

Solutions:

    • Make sure you have roughly 50% of the pond in a variety of aquatic plants.  This will also bring up the CO2.
    • There isn’t much you can do about more sunshine unless you have a sail shade over the pond that you can remove. 
    • If there is not enough circulation consider adding a 5 foot stream with several small waterfall drops. 
    • Make sure the pond is not overcrowded with fish.  100 gallons supports about 10 inches of fish.  Go to the Pond Calculator to see how many fish your pond will support. 

Microbial ALgae

Might also be referred to as Pea Soup Algae, Green Water Algae, Cloudy Water, Planktonic Algae, Plankton Algae, or Suspended Algae. Scientific name is Phytoplankton
This type of algae can’t be grabbed by hand.  It is suspended in the water. 

Causes:

    • Runoff from the yard, specifically from fertilizers or weed killers (they can kill off the beneficial bacteria and disturb the balance in the pond AND that type of run off can kill the fish.)
    • Excess nutrients
    • You may be feeding the fish too much. 

Things to know about Microbial Algae:

    • an Iongen will not help with microbial algae.

Solutions:

    1. Stop feeding the fish.  See the guidelines in How to Feed Your Pond Fish for help.
    2. Put in Flocculant and put in a fine filter pad into the skimmer basket.  This will cause the suspended algae to clump somewhat and can then be caught in the fine filter pad.  The pad will need to be removed every 1/2 hour, then every hour, then every 2 hours and rinsed, otherwise the pump will be starved of water.  This is a hands on exercise! 
    3. Improve oxygenation by adding some aerators. (please note, I recommend the 2 stone aerator and not the 4 stone!  I have found the 4 stone aerator breaks more quickly. )
    4. Provide shade.  Lilies installed this year will help next year but for now, you may need to put up a sun shade or patio umbrella. 
    5. Add extra beneficial bacteria. Powdered is best or use Aquascapes “Clear Water Treatment.”
    6. The fastest way to treat it is to put in a UV light.  A pressure filter with a UV light seems to keep microbial algae under control when the ecosystem can’t be in balance. Keep in mind, this sterilizes the water and kills beneficial bacteria.  It is better to treat the causes for a long-term solution.

DIATOM ALGAE

Might also be referred to as or peanut butter algae
It is hard to show this in a photo.  I’ll have to take another picture when I run into it again.  It covers all the rocks, looks like peanut butter slime and may have bubbles in it.  Can be in the pond or waterfall (or both!)

Causes:

    • Imbalance  pond. Excess nutrients
    • Too much copper in water
    • Iongen or Ionizer turned up too high when no string algae present. 

Things to know about Diatom Algae:

    • an Iongen will not help with Diatom algae, it will make it worse.

Solutions:

    1. Turn off the Iongen or ionizer
    2. Do a partial water change if there are fish.  No fish?  Do a 100% water change.
    3. Pressure wash it off to start over.
    4. Get on a regular and consistent bacteria treatment plan.  Once a week! Powdered is best.

Chara ALGAE

May be referred to as skunk weed, musk grass, or stonewort.
Chara grows from the bottom of the pond

Causes:

    • Imbalance  pond. Excess nutrients  (phosphorus and nitrogen)

Things to know about Chara Algae:

    • I see this in larger ponds that have less circulation, no gravel on the bottom of the pond.  There may be fish, but very little addition of beneficial bacteria and if there are plants, there are not enough for the size of pond. 
    • It seems like and aquatic weed but it is, in fact, algae.
    • This algae is filtering the water and using up excess nutrients.  It actually keeps the water clean and clear! 
    • It grows from the pond floor.  Once it reaches the top of the water it can look really bad.  It is fibrous and crunchy and smells musky.  

Solutions:

    1. This can be raked out periodically. We use a certain aquatic weed rake that can be thrown out into the pond and pulled in with a rope. 
    2. Liquid algaecide containing copper – but beware, this will also kill other floating plants and can be detrimental to fish if used improperly. 

Gel Balls - Clearish

Also called Spray or pour peroxide directly on the Nostoc.
Photo of gel blobs called Nostoc in water
Photo of gel blobs called Nostoc in water
Photo of weird algae in waterfall like gel blobs called Nostoc

Causes:

    • Imbalance  pond. Excess nutrients -Mineral-rich water

    • Constant moisture on rock surfaces

    • Slow-moving water tricklingly over waterfall rocks

    • Low competition from other algae or plants

Things to know about this gel like stuff:

    • These dark jelly-like things appear on wet rocks where water slowly flows.  It can look like little clearish or black gel type balls.  
    • It’s actually not algae!  NO!   Apparently it is “Nostoc Cyanobacteria”. These are little colonies! 
    • It can be difficult to eliminate
    • It is harmless! It simply has an unusual appearance.

Solutions:

Turn off the waterfall pump and use a stiff brush or pressure washer to remove the colonies.

    • Use 1 part pond water, and 1 part 3% hydrogen peroxide. Put it in a spray bottle or garden sprayer.

      Spray or pour peroxide solution directly on the Nostoc.  Hydrogen peroxide oxidizes the gelatin layer and kills the colony.

    • Let it sit 10–15 minutes. It may turn gray/white.

    • wash area down with water after treatment and turn on the pump.
    • Clean out the whole pond to remove the biomass before restarting the pump.

Remember that when the rocks are perfectly clean, no green AT ALL the beneficial biofilm has been removed, allowing the Nostoc to thrive. There needs to be beneficial biofilm to act as  competition for resources to keep it away.

Instead of keeping rocks perfectly clean, allow normal green algae biofilm to grow.

If possible, change rock layout/waterfall so water runs faster over surfaces.

What NOT to Use

Avoid harsh chemicals such as:

    • Chlorine bleach

    • Copper algaecides

    • Strong herbicides

(These can harm fish, plants, and beneficial microbes.)

Algae - is it really the bad guy?

Pond algae is Mother Nature’s way of helping out.  It appears when there are excessive nutrients in the water.  Algae serves to consume it when the aquatic plants can’t keep up with the nutrients. 

If we don’t want to see excessive algae, we have to help keep the ecosystem in balance.  Understanding that some amount of algae is not a big deal and is part of a healthy system is important.  A pond’s ecosystem has seasons just like the weather.  Algae blooms will come and go with the seasons.

Through it all, we need to support healthy, Living Water.

What do other sources have to say about Algae:

Read more about ponds HERE and if you think your system may have a leak read THIS.