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.

Soil Science for Gardeners book 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.

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. Nice Info. Thank You! Kinda like being new to spa maintenance, the companies would have you have 50 chemicals on a shelf and checking your spa water every 2 hours around the clock dumping this and that in around the clock when all you need is 4 chemicals for maintenance and a once a week check. Too many companies out their not selling honest. Always have to be careful when venturing into a new project.

    Anyhow I have a 50′ x 80′ x 5′ deep impoundment pond. I have recently stocked it with bluegill sunfish and minnows. Going to add 10 catfish and 10 bass to it this fall. I have a windmill aerator up on the damn, I put a couple downed trees in there for fish structure, I let nature take its course with plants that grow around the pond and in the waters edge. I do have string algae (moss) but this seems to come and go with the seasons. And this is what led me to your article, “OMG do I got to get rid of it?” Well I’m thinking not especially after reading your article.

    Hoping that just letting Mother Nature take her course will leave me with a nice little community of natural nature.

    Thank You Robert

  2. I like what you put together here and agree, mostly. But, you’re missing one big thing in terms of why ponds don’t have enough beneficial bacteria, at least in bigger ponds to dissolve the rotting organic matter at the bottom. Over years in an unmanaged pond, there will be layers of this stuff building up. It’s not because of chemicals, it’s unmanaged. It could be more than a foot thick of ‘muck’.
    The reason is, this good bacteria needs oxygen to survive. As the bacteria does it’s thing, it gives off a byproduct of toxic gas and creates an oxygen deficient zone right where it needs it most, at the bottom. Then it dies off. Another layer is formed.

    An aerator is what missing in this case to keep the beneficial bacteria thriving. It solves the problem in two ways, adding oxygen, and moving water. As the air bubbles rise, it takes a current of water with it and new water fills the void.
    The thing about adding beneficial bacteria at this point, say in the form of a pellet whisping away into the murky bottom, it speeds up the process by injecting bacteria right where you want it as it.

    I’ve observed the scenario I described reverse decades of built up muck in two years time, to a now hard sand bottom. Not saying it wouldn’t have happened with the Aeration help alone, just not that fast.

    I wouldn’t put beneficial bacteria in a myth category that does nothing.
    It helps.

      • Hi Robert,
        Actually I did do a study that supports my claims.

        I see that is a common request you make. Let me ask you this, if I were to present for you. Would you review it with an open mind and consider updating your claim that it’s a Not waste of money?

        for the record; I am not affiliated with any pond product suppliers.

    • My Koi pond is almost 8000 Gal. in full sun, with a Bog filter and 90 F days. No string algae. There is no muck on the bottom – all muck is in the bog. Aeration is vigorous. No string algae, but summers make for green water. Ergo, I think I need more surface areas for bacteria. // The “modus operandi” for business profit is to Sell, sell! – so I do believe adding bacteria is a Myth. Your Post presumes “muck” on the bottom, and therefore is not “scientific.”

      • “Your Post presumes “muck” on the bottom, and therefore is not “scientific.”” – First of all it does not presume muck on the bottom, and even if it did, that would not make it unscientific.

  3. i have a pond filed with about 100 koi fish and have a problem with algae pls advice have about 16k litres of water pond area , thks

  4. You are misssinforming your readers.
    What you are saying could be compared to the human body white cells fighting infections. Although the body can often overcome it itself, it is not always the case and sometimes it needs help because of coexisting factors. But depending on your beliefs, you could always wait it out and see… good luck with that.
    We inherited a pond without any water intake, that had been gradually getting heavier and heavier muck. Many trees around it.
    Aeration and plantings alone was not enough. Introduction of beneficial bacteria saved the 50×50 pond over the course of two years. We now see the bottom. Had we waited it out, there would be grass now where there once was a pond.

    • If you think I am wrong, post a link to some scientific data that proves me wrong.

      just because you used the product and your pond got better does NOT mean it wouldn’t have gotten better on its own. Without a control, you can’t reach any conclusion.

  5. Hi we made our pond around 500 gallons have a water pump and about 24 small goldfish I’ve tried bacterial essentials yesterday morning and now nothing it’s still murky green am I just being impatient? Just want to see the bottom of my pond please help

    • Elizabeth, you put Beneficial Bacteria in and you expected it to be better the next day? I’d say that’s a combination of being impatient to the Max and misinformed.
      I suppose my pond is somewhere in the 1000-1500 gal size and in my area there weren’t many with ponds when I began in 2004. I received lots of bad info in the beginning like this Lagoona filter is all you’ll ever need! lol I use that filter as an in-pond pre-filter now after building my own setup consisting of two 50gal drum 3 stage bio-filters. I used a UV light at one point but not in years and yes I have used Beneficial Bacteria and find it very useful. A Google search for Beneficial Bacteria is what lead me here today. Robert is right, too much sun, fish feed, feces, etc lead to an unbalanced ecosystem.
      A well balanced pond with the right combination of plants, filtration, fish, feed, and basic maintenance can almost sustain itself. In the case of your small pond I imagine it is anything but balanced. Do your research or higher someone who knows what they’re doing it’ll save you a lot of frustration and a huge learning curve! lol A small heats up easily so it needs a little shade stick one of those deck umbrellas in the ground on the south side during the afternoon heat or try stringing one of those triangle shaped shade sails overhead. My pond’s East side is butted up against a huge 110 year old lilac bush which shades it from much of the morning Sun. I have lilies, yellow flag Iris, Arrow Heads, etc. A homemade pump support that sits in the center of the pond with a homemade fountain and a $37. Amazon air pump to aerate the pond. It’s been going a couple years now, two winters! Robert is entitled to his opinion after all it’s his blog lol Personally begin using Beneficial Bacteria in the early spring to load up the Filtration system which has been disconnected and dry all winter. Reaches -20C here haha and I add some Beneficial Bacteria every week. It works for me I have my issues with string algae but not so much with the Beneficial Bacteria. You added it yesterday and expected success in one day? lol As I said it takes a month to fully load up the bio-filters. Good Luck.

      • I am not an expert or have experience with pond management but my late grandpa’s organic pond(20x40ft), not cemented and no rubber liner, just natural. 53 years on and last time I came for a visit, it is still there. Just like the one in the picture. The pond was already there before I was even born.

  6. I think you are talking about well planted wildlife ponds here in warmish climates with very few fish – if any – here. Fair enough -not everyone actually keeps Koi or even goldfish so you probably don’t understand why people use beneficial bacteria. However, if you speak to people who keep ponds with goldfish or the even more demanding Koi they’ll explain why adding beneficial bacteria works under certain circumstances. Obviously fish stocking levels relative to pond size are very relevant here. First, if you live in a temperate climate then because the fish are hibernating over winter and the water is cold even if you leave your filter running the number of bacteria in the filter system will be very reduced indeed. Aerobic bacteria need air and food to survive, So adding beneficial bacteria – especially some of the special strains that work in cold water at low temperatures about 8 degrees C in spring – as you start feeding will effectively jump start the pond and considerably speed up the process of bacteria re-establishment. It doesn’t matter if you add them to your filter system or your pond but if you have a UVC then turn it off for the recommended number of days. Since you should have given your filter system a good spring clean anyway you will speed up natural processes of bacteria re-establishment within the filter .Once a year in early Spring when water hits about 9-10 degrees C is therefore usually enough. The two other times beneficial bacteria are worth adding. The first is usually in early spring if your regular water tests begun in spring show problems with water quality (ammonia, nitrites and nitrates) or you have very greenwater ( which shows lots of nitrates). The problem here is that the pond bacteria are not establishing quickly enough and plants are also not growing strongly enough yet (if your pond is covered in duckweed then that will also stop greenwater but fish people tend not to like this). In this case you can certainly bring ammonia and nitrites down effectively by adding additional bacteria – it is generally much better for your pond than using chemicals to kill the algae and there are complementary preparation that contain the anaerobic bacteria that will breakdown nitrates which can be added afterwards. All you are doing in adding additional bacteria is speeding up natural processes. In case you wonder why you seldom get algae problems in ponds once summer arrives here is how the science works a) plants are growing strongly and using up nitrates and phosphates and b) aerobic bacteria have reached a natural balance at their maximum. The other time it is worth giving the filter and pond a boost of beneficial bacteria is when you add fish to the pond from your quarantine pond/container. This will of course depend on size of pond, existing stocking level and size of new fish.More fish meets more waste so adding bacteria will help flatten any ammonia or nitrite spikes and helps the pond catch up more quickly Obviously what I have said here is only relevant to fish ponds where you are keeping animals and which you have an ethical responsibility to look after them as best you can. In wildlife ponds you certainly don’t need to bother with all this as their inhabitants probably have minimal bio loads and the duckweed or pond weed will do the job for you until the pond plants take over. While as an fish keeper I certainly use beneficial pond bacteria to aid my fish I also have a wildlife pond and in the twenty years that it has existed I’ve never added bacteria to it. Things are also different in tropical environments as the beneficial bacteria tend to stay at a constant level as the fish don’t hibernate and stop eating.

    • You are missing one key point. The bacteria, even the cold hardy ones, are already in the pond. If fish waste levels increase, so do natural bacteria levels. In fact, bacteria reproduce at extremely fast rates.

      The only time you would need to add them is if you chemically kill everything in your pond.

  7. Hi Robert, I have a 6,000 gallon pond and drain and clean it every year. Inevitably, I do a daily battle with string algae. Do you think adding koi fish would help? I don’t want to get looped into the good bacteria/algaecide cycle. Thanks, Julie

  8. As someone who manages ponds of a living I can tell you from experience your information is wrong. I’ve seen good bacteria turn ponds around. Big and small ponds. In fact one of the biggest things we do on large ponds is bacteria socks and it clears it up and the results are measureable. It seems to me you just wanted to state your opinion as fact.

    • Lots of people have successful ponds without adding bacteria. Therefore they are not needed. It is not my opinion that bacteria are everywhere – scientific fact. But if you have some references supporting their use – I’d be happy to look at them.

  9. I was thinking of this also, can I bacteria thrive in a close bottle without nutrients? since beneficial bacteria sold at petstore was place in the bottle


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