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Beneficial Pond Bacteria – A Waste of Money

I was reading some gardening Facebook posts and a lady said she buys beneficial pond bacteria for her pond and adds them weekly. WOW! That was news to me. I’ve had a man-made pond for over 8 years that works just fine without added bacteria. I must be missing something important?

Truth be told – I smelled another gardening myth. Let’s have a look.

Beneficial pond bacteria for ponds - koi

Beneficial pond bacteria for ponds – koi

Building Natural Ponds

Before I dig into this topic I’d like to add a shameless plug for my upcoming book, due out in May, 2017, called Building Natural Ponds – Create a Clean, Algae-free Pond without Pumps, Filters, or Chemicals.

Beneficial Pond Bacteria – The Rational

Algae can be a big problem in most man-made ponds. It grows when there is too much light, and too many nutrients, especially nitrogen and phosphorus. If you reduce the level of nutrients, algae will not grow as well. Problem solved.

So how do you reduce nutrient levels? The answer is really quite simple – you make sure that the pond contains a lot of beneficial bacteria. Beneficial pond bacteria also need nutrients to grow and they will out compete the algae for nutrients.

So far so good. This is a simple system that is known to work well.

To make this work you need to have enough beneficial bacteria. What is the best way to get them? From a manufacturers point of view that is obvious. Grow them, package them and sell them to pond owners in a fancy jar with a fancy name: ‘Beneficial’ pond bacteria.

Consider an average sized pond that is 10 x 10 x 2.5 ft, which is about 2,000 gallons. The first product I found on the internet was $30 US to treat this pond for 12 months. They also have the supper strength stuff at $60 US for 12 months. It’s not a lot of money, and if it is needed most pond people will pay this – every year.

What Are Beneficial Pond Bacteria?

There is no clear definition for this but essentially any mixture of bacteria that would decompose organic matter, use up nutrients and live in water would fit the bill.

The beneficial bacteria that are being sold are natural bacteria. We are not talking about expensive genetically modified bacteria. We are talking about the same bacteria that can be found in any natural pond. There are probably millions of species that would work just fine.

Adding Bacteria to The Pond

What happens when the beneficial bacteria are added to the pond? The bacteria will have a look at their environment and if they like it they will start to grow. As they grow, they consume nutrients and divide (ie make babies). In fact they can multiply very quickly – in the lab some bacteria double in number every 20 minutes.

As the number of bacteria increases, the amount of nutrients decrease. At some point there is not enough food for everyone and they start to die off.

It is important to understand that there will always be some food in a pond and so the bacteria never die out completely. Their numbers just get less. In fact the ones that die will provide nutrients for the ones that remain. Bacteria are cannibalistic.

Where Do Bacteria Come From?

Everywhere! They are in the air, water, soil, on plants, on fish, on fish food. Even before you add water for the first time to a new pond, the liner is covered with bacteria. The reason for washing your hands regularly is because they are covered with bacteria. Even wiping your kitchen counter with a disinfectant will not remove all the bacteria.

You can’t keep bacteria out of the pond.

Natural Bacteria in The Pond

The natural bacteria in your new pond do exactly the same thing as the ones you buy. They have a look around their environment. Some might not like being in water and they die. Some don’t like the temperature or pH and they either die or at least don’t multiply very much – they are waiting for conditions to improve.

A new pond has very few nutrients so bacteria don’t grow well for a while – but either does algae.

But in no time at all fish poop. Insects and birds drop organic mater in the water. It does not take long before the nutrient levels build up. As they do, bacteria start to flourish. You can see them as a coating of slime on plants, rocks and the pond liner. To you this is icky stuff, but to the pond this is a natural water purifier.

Why Do You Need To Add Bacteria?

Unless you do something to kill all of your natural bacteria you do NOT need to add more. Want proof? Have a look at Pond Pumps & Pond Filters. I put this man-made pond in 8 years ago. It has no filtration, no air pump and no chemicals. It does have a lot of plants and a lot of surface area (small rocks) for bacteria to live on.

Natural pond with no pumps, filters or added beneficial pond bacteria, by Robert Pavlis

Natural pond with no pumps, filters or added beneficial pond bacteria, by Robert Pavlis

You can do things to kill off your bacteria. If you add an algaecide, it will kill off bacteria (ref 3). Chemicals for adjusting pH will also harm your bacterial herd. If you recycle your pond water through a UV system you will kill bacteria.

Emptying your pond and scrubbing the sides to get it clean also kills your herd. This is recommended by many people and makes no sense at all. Why remove the slimy coating that is home to your natural water purification system?

If you did these things and killed your bacteria it might make sense to add purchased beneficial bacteria to get your bacteria numbers up quickly. Or you could just wait a day or two for them to start growing on their own.

Keep in mind that adding chemicals like copper based algaecides are long term problems. The copper does not go anywhere, unless you do a water change. As long as it is in the water it will affect the bacteria. Maybe this is one reason that companies who sell algaecides also sell beneficial bacteria and recommend you add them weekly. Their algaecide keeps killing off the bacteria so you have to keep buying more and more bacteria. Sounds like a good business!

The Commercial Bacteria Myth

In the words of one manufacturer “the  addition of beneficial pond bacteria will render the pond clean and clear”. Is this true or is it a myth?

It may be true.

If for some reason you have killed off your bacterial herd, adding more from a jar will speed up the re-population of bacteria in your pond.

But this is only true if the following two factors are working in your favor.

Are The Purchased Bacteria Alive?

The bacteria in your purchased bottle need to be alive for them to work. You really don’t have an easy way to test this. One commercial source said that “live bacteria smell” and if the contents of your container doesn’t smell – they are dead. That is not very reliable. Besides dead rotting organic material (ie the bacteria) tends to smell!

Are The Bacteria Matched To Your Environment?

Every pond has a different environment with variations in things like water hardness, pH, temperature, existing microbes, nutrient levels, etc. The bacteria you add will only grow well if they like your environment. You can’t tell that by reading the label.

Natural vs Commercial Bacteria

The main argument for adding commercial bacteria is that the pond does not have enough natural ones. What would cause such a situation?

Other than added chemicals the two main reasons would be a lack of nutrients and a lack of substrate for bacteria to live on – the rocks and pond liner.

If your pond does not have enough nutrients for you native bacteria to grow and prosper, then it does not have an algae problem – there is no problem to fix and adding a commercial product is just a waste of money.

Substrate is the surface area where bacteria like to live. In commercial filtration systems this is usually some kind of sponge, or small pieces of plastic. Both of these provide a large surface area on which bacteria can colonize. The key here is the large surface area.

In a pond bacteria like to grow on the pond liner, on plants and on the surface of rocks. A properly designed pond will provide a large amount of surface area, usually in the form of small rocks.

If the pond has lots of places for bacteria to live then the native bacteria will already be living there. Adding more commercial bacteria will not increase the population.

It seems to me that if your pond lacks bacteria it means your pond does not have the environment needed by bacteria to live. Adding more from a jar is at best a short term solution.

Beneficial Pond Bacteria – A Waste of Money

Unless you do something to disturb your native bacterial herd I see absolutely no reason to add beneficial bacteria. The bacteria you already have are just as beneficial as the ones you can buy.

Aquascape sells a product that contains 1 billion bacteria per gram.  One gram of healthy soil – the weight of a paperclip – can also contain 1 billion bacteria. If you feel the need to add bacteria just add a pinch of soil.

When I reviewed commercial products I noticed a lot of claims, but not a single piece of evidence to support the claims. There was not a single study to support the use of their products. However, a scientific study that I did find looked at adding a commercial bacterial product to ponds (ref 2) and found little difference in water quality between treated and untreated ponds.

Adding commercial bacteria to your pond to keep the water clear is a waste of money.


  1. Primer About Ponds and Microbes;
  2. Effects of a Bacterial Inoculum in Channel Catfish Ponds;

  3. Copper Algaecides and Beneficial Bacteria;

  4. Photo source: AgnosticPreachersKid



Robert Pavlis
Editor of
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

11 Responses to 'Beneficial Pond Bacteria – A Waste of Money'

  1. Sandi says:

    How do you deal with black/crown rot?

  2. Brian Tremback says:

    It’s important to differentiate between heterotrophic organisms, like bacteria that break down organic compounds, and autotrophic organisms, like algae that synthesize from inorganic compounds and sunlight. Bacteria (unless they’re cyanobacteria that photosynthesize) don’t compete with algae. Bacteria actually provide algae with the inorganic nutrients they need by recycling the organic matter into raw material for algae. While cyanobacteria (blue-green algae) is an competitor with algae, many species produce toxic compounds.

    Plants, especially those that extract nutrients directly from the water, can reduce algae because they directly compete with algae for nutrients. They also reduce the amount of light available to algae for photosynthesis.

    • Why does this distinction need to be made?

      Both types of bacteria need nutrients like nitrogen and potassium. They may get them from different sources, but they still need them. As heterotrophs grow and multiply, they remove these nutrients from the water, and prevent them being available for algae. Is it a case were they produce much more free nutrients than they ever use themselves?

      I assume that the commercial beneficial pond bacteria are heterotrophs since their function is to reduce ammonia levels and organic levels. One could then argue that their effect in a pond is to convert organic matter into nutrients that algae can use.

      • Brian Tremback says:

        The distinction is important because of the claim that bacteria will reduce algae in the pond. One of the main metabolic lifestyles of bacteria, heterotrophy, is to break down organic matter into its constituent inorganic compounds, like nitrates and phosphates. They provide algae with the inorganic nutrients they need to grow, just like the bacteria in a compost pile decompose kitchen scraps into plant-usable nutrients. Once all the organic matter is decomposed, heterotrophic bacteria populations will plummet. At least until plants, algae, cyanobacteria, etc. use minerals and sunlight to make more organic matter. Nutrients aren’t removed, they’re just borrowed.

        Although cyanobacteria are autotrophs and have the potential to reduce the population of algae by competing with them for nutrients and light, they also have a negative aesthetic appeal (scums, coatings, opaque water). Moreover, some produce toxic compounds and others fix nitrogen, so there’s no advantage in substituting cyanobacteria for algae if you want a clear and clean pond.

        • I understand the point you re making, but do heterotrophic bacteria not also need nutrients? They need nitrogen and phosphorus to grow. Which means that they must also be competing with algae for these nutrients.

          Is it a case that they produce more nutrients than they use?

          • Brian Tremback says:

            Bacteria certainly tie up nutrients in their own bodies but, as long as there’s a food source, they’re excreting a continuous stream of molecules that become available for autotrophs.

            We know that a healthy population of heterotrophic bacteria in our gardens benefit the autotrophic plants. Isn’t it reasonable to assume that bacteria in a pond would benefit the algae?

  3. Roger Brook says:

    I have two quite large fifteen year old ponds that are crystal clear. I have watched their very different ecologies evolve over the years and like you I have no filters, pumps or other contraptions. Nor have I ever cleaned them other than dragging out surplus organic debris with a lawn scarifier.
    I am sure I will agree with everything you say in your coming book!
    Not having really considered it I have never thought about pond bacteria! Thank you for enlightening me of their significance.
    Like you I abhor the gullible being exploited by selling them bacteria!

  4. Rick Wiebe says:

    I add benificial bacteria in my pond when my koi are spawning. It brings the ammonia levels quicker than if I allow it to go unchecked. My three females are 28″+. They do lay a lot of eggs. I have 25 koi above 12″ and they do affect my water quality. For string algae this year I tried a product. In my 3500 gallon pond I used 5 ml. of product and in 7 days the string algae was gone. I did one dose a week for 4 weeks and then stopped. This took place in the month of May 2016 and it is October and still no string algae. I would have three feet of algae hanging off all the rocks in my stream.

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