Beneficial Pond Bacteria – A Waste of Money

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Robert Pavlis

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

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.

Growing Great Tomaotes, by Robert Pavlis

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.

Plant Science for Gardeners by Robert Pavlis

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 ponds promotional ad

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.

Related Topics

Winterizing Ponds and Water Features

Water Lilies for Ponds

Pond Pumps & Pond Filters

Selecting the Right Pond Liner


Building Natural Ponds

This blog post is the second most popular post ever on this site. Lots of people comment and are interested in more information about building natural ponds, so I have started a public Facebook Group to make it easier for people to discuss this hot topic. Please join the group at

Building natural ponds face book group
Building natural ponds facebook group


  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



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Robert Pavlis

I have been gardening my whole life and have a science background. 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!

53 thoughts on “Beneficial Pond Bacteria – A Waste of Money”

  1. Thanks for your blog. Am definitely going to save my money now. Your post reminded me of an old livestock trough in the garden of a property my parents bought when I was a kid. We cleaned it out as it was full of weeds. I think it had been left untouched for a decade or so. We were super surprised to find it was also full of fish, so ended out removing about 3/4 of the weed and then leaving it alone. Fish never got fed and everything seemed to be self-supporting. Now, 45 years later I’ve bought a property with another old livestock trough in the garden full of waterlilies and really rotten murky water. Have cleaned it out and reintroduced some of the waterlilies, other aquatic plants and a lot of rocks. It has a small fountain and no filter, and I’ve put about 5 small fish in. I was wondering about how to keep it clean, so I’m really glad I found your blog.

    • They don’t get killed by winter – they just become dormant and grow again once temperatures reach their ideal conditions. UV will harm them but it will also kill the new ones you add – so why bother adding them with UV?

  2. Alright listen, if theres something bacteria can eat, you’ll find it there, this is pretty well known.

    Can a pond have more plant material and fish poop than there is bacteria to eat it, yes. Is it only a matter of time until the bacteria catches up, yes. Can the water conditions be more favourable to the fish than the bacteria, yes. Does bacteria adapt to its environment, yes. Willa dog living on an island with only fish to eat eventually develop fins, yes probably, over the course of likely hundreds of thousands to millions of years.

    Can you speed up that process by adding more dogs to the island, yes.

    See where im going with this?


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