Algae happens – what you can do about it:

Did you know that algae is actually a part of the ecosystem?  Yes it is!  When there is a bit of algae in the pond, it is okay.  What we don’t want is for that algae to become an eyesore that takes away from the beauty of the feature.

There are literally thousands of kinds of algae.  We are going to categorize it in the simplest way possible.  You can also compare your algae to the algae in our ALGAE GALLERY!

  What it is Possible causes What to try  
Green cloudy water Microbial Algae

Overfeeding fish

Unbalanced Ecosystem

Lack of beneficial bacteria

Too many fish in pond

Recent heat wave

Try cutting back on fish feeding.  Click HERE for more information on fish.

Try adding plants like floating hyacinth and floating lettuce for natural filtration.

This suspended algae can also be captured by adding a very fine filter to the front of the skimmer for a day and then removed.

Adding Flocculant helps because it causes the algae to bind together, making it easier to remove from the pond.

Clear water that is tinted green Short green algae on rocks makes water look green.

Ecosystem is on the way to being balanced, but isn’t quite there.

Lack of beneficial bacteria

Too much nitrogen in pond

Recent heat wave

Try adding lots of plants, like floating hyacinth and floating lettuce for natural filtration.  They will use up the extra nitrogen.

Bump up your beneficial bacteria by adding it every 3 days for a couple of weeks.

Remember, it can take consistency and time for a pond to get into balance.

String algae String Algae

Overfeeding fish

Unbalanced Ecosystem

Lack of beneficial bacteria

Too many fish in pond

Installing an Iongen can keep this at bay!

Remember, if the string algae is pulled off without treatment of algaecide (use very cautiously) it will spread!

Brown or tea colored water Tannins

Leaves decaying in pond and other debris create tea colored water

If driftwood has recently been added, the tannins may be washing out.

If it is from leaves decaying, the pond needs a cleanout.

Activated Pond Carbon (charcoal) may be helpful.

If its from driftwood, a water change may help. It can take months for it to subside.


Slimy brown/gold algae like a film that covers gravel and rock

It may bubble


Not enough water movement and aeration

Not enough beneficial bacteria

Rock that is high in silicates (Flagstone)

Lack of fish

Pond out of balance

Work to get pond balanced using the 5 Elements of a Healthy pond.

(bleach and shock treatment does not work!)

Call Colorado Pond Pros right away!

Black water Heavy, deep organics in pond Large amount of organic matter decaying in pond. Pond needs a cleanout  
Foam in pond

Off-gassing of liner

Kids threw something in?

Fish are spawning?

Off-gassing is very common to newly built or relined ponds.

Fish spawn generally in the spring.  They may seem aggressive towards one another.

Add Pond Foam Free, use for 3 weeks.

Tell kids how important it is not to put anything in the pond!

The fish will stop spawning and it will go away.


String algae is fibrous. Sometimes it’s referred to as hair algae.

Algae blooms occur in early spring when temperatures begin to rise. This happens because other life in the pond is still a bit dormant.  Without all aspects of the ecosystem contributing to the health of the pond, algae can go to town! Beneficial bacteria and plants wake up slightly later than the algae does in the spring.  Algae may crop up right after there is a big rainstorm. Water runoff from the yard may contain other agents that throw the pond out of balance.  A heavy fish load or lack of plants can contribute to string algae growth as well.

Diatomacious Algae
The top picture shows microbial algae before a cleanout.

Algaecide – Beware – Uses and Cautions

Algaecide may seem appealing and is useful in some situations, but know that while it may quickly kill off algae, it can quickly kill off your fish too. Be sure to read the instructions carefully and call a professional if you need help.

Algaecide works by removing the oxygen and suffocating the algae.  It is also hard on plants, beneficial bacteria, and fish.  Algae itself puts oxygen into the water. For that reason we recommend only treating ¼ of the pond at a time.  When treating algae in a waterfall, turn it off and sprinkle dry algaecide onto the area, leaving it sitting without the waterfall on for 30 minutes.

The day after using algaecide, make sure to add beneficial bacteria to either replace what has likely been destroyed or to add it if it has been absent. The dead algae may float on top of the water and get stuck in the skimmer basket.  Make sure to clean it out! When large amounts of algae are present, we know that the balance of the ecosystem is off.  Getting it back in balance will help your pond look beautiful again. Algaecide can destroy good parts of that system so the beneficial bacteria needs to be replaced several times after a treatment.

If your fish are coming to the top of the water and seem to be gasping for air after an algaecide treatment, then too much has been used and you are at risk of losing fish. Do a partial water change, adding detoxifier for protection of the fish.  You can also put in an aerator to get more oxygen flow going and hopefully keep the fish from dying.

Remember that overuse of algaecide can cause future outbreaks of algae — worse than the original problem and it can damage plants and fish.  If it is necessary to get control of algae, follow the directions to the letter and make sure to get the pond into balance after its use.