Is There A Secret To Pond Algae Control?

String Algae

A few years ago a book called The Secret hit the shelves and everyone was talking about it. If you haven’t read or heard about it, it involves something called the law of attraction. Or simply, you attract what you think about.

Now, I know what your probably thinking…he’s going to tell me to think about having a clear and clean pond in my mind and my algae problem will go away.

Uh, no…that’s not quite where I’m going with this, but you’re welcome to try that and let me know how it goes.

Actually I wanted to address the word “secret” and how it creates this mystery in the mind. What’s funny is that in the secret, they talked about some pretty obvious things. Things that have been written about for thousands of years, such as those found in the bible and other scriptural text.

In some ways, “the secret” wasn’t really such a secret after all. And I’d suggest that the same thing applies to pond algae control in your pond.

Sometimes the secret can be pretty obvious, once you know what to look for.

Here’s a couple examples from some conversations I had with pond owners this week.

One gentleman had a very large pond, nearly 9 acres in size, and had algae develop around the edges and the shoreline. This wasn’t a constant problem, and the pond usually stayed very clear, but the algae problem had come up only recently, after an unfortunate incident involving his septic system for his home.

A lady also emailed me with an algae problem in her small backyard pond. Normally she had never had a problem but algae has been terrible this year, and came up after they fertilized their yard this spring.

In both of these cases, I explained that algae, like any other plant, needs certain things to grow well. Sun exposure helps a lot, but above all things, nutrients in the water help algae grow more than anything else.

The issue of high nutrient loads in a pond can be traced to many things and sometimes they may have a singular primary source, but most often they come from a number of things in and around the pond’s environment.

In the examples above, we can specifically identify a leeching septic system and run off into the pond from fertilized ground. Both of these things, when added to pond water will definitely help algae grow.

So here’s the big “secret” to pond algae control.

Identify the root cause(s) that are helping that algae grow well.

When you do this, and then attack this root cause in some way, in many cases, algae will go away after a time.

So rather than treat the present algae with a chemical or spend a ton of time and money on other treatment options, it makes more sense to spend the money and fix a leaking septic system or look for another way to help your lawn grass grow rather than to treat it with fertilizer.

If you have green water, and you suspect that maybe you have too many fish in a pond for it’s size, be sure to work at reducing the number of fish in the pond. Here’s a helpful ratio by the way that I’ve probably mentioned before…plan on needing 10 gallons of water for every inch of goldfish and up to 25 gallons of water for every inch of Koi. If the total fish load in a pond is above these ratios, then your fish could very well be the leading cause of your algae problem.

If you find a lot leaf debris in the pond, do your best to minimize this if you can. Covering the pond with netting in the fall may help with the leaves are flying off the trees. A good skimmer system in smaller ponds can help keep them cleaner.

Does your pond get a lot of sun exposure? If you can add some floating plants to help shade the pond a bit more or research the use of aquatic dyes for larger ponds as these can sometimes prove helpful.

And of course, I’m often in favor of using good, common sense solutions like beneficial bacteria or good filtration to help a pond recover it’s balance or to help it stay that way.

But above all things, rather than looking for the quick fix, secondary solution to your algae problem, take some time to really think about why that algae might be there in the first place. What could be it’s root cause? If you can apply a bit of detective work combined with the knowledge of what algae needs to grow, you can likely pinpoint the very specific reasons why the algae is there to begin with.

And when you do, you’ll have the secret…if there really is such a thing, to true and lasting pond algae control.

26 Responses to Is There A Secret To Pond Algae Control?

  1. gardenponds by ray May 6, 2009 at 11:34 pm #

    Thanks Mark you give good advice for pond owners .thanks Ray Collins PA

  2. John Hendrickson May 7, 2009 at 3:05 am #

    I agree with everything that you have said but would like place more emphasis on the function of the pond filter. As I understand it the filter collects the dead algae and the bacteria digest the algae in the filter so in one respect it works like a sceptic system.
    the dead algae are consumed by the bacteria and that is why I add bacteria to my pond once a week. Please tell me if I am wrong!

  3. Mark May 7, 2009 at 3:45 am #

    Hi John,
    Most certainly good filtration is essential, particularly if the pond has fish in it. You are right on with your understanding of a biological pond filter and how it works.

    I must say though that there are times when even good filtration may not keep up if environmental conditions or fish overload take place. There are limits to everything including filtration.

    So in a sense my effort with the article is to be sure to do all the common sense things that are recommnded, yet when you have an algae problem, all is not well or working right and the best route to take is to look for the real reason that algae is there to begin with.

    To me, this makes more sense as an initial step than spending more money on added filtration, additives and all of that stuff.

    I realize this might seem to be an odd stance to take for someone that sells pond care products, but I sort of feel that common sense and some honesty should trump everything else.

    Thanks as always for your comments.


  4. Rene May 7, 2009 at 3:53 am #

    I have been skiming my pond every day to remove leaves and debris to date it looks good thank you for your advise Rene

  5. cath18 May 7, 2009 at 4:32 am #

    Thanks Mark for the advice. Exploring the root cause can definitely save us a lot of money and anxiety.


  6. David Marney May 7, 2009 at 5:18 am #

    Good advise , thank you.. We had a bird feeder just a tad uphill from our pond early on =took me 2 seasons to figure out why my pond looked more like a sewage treatment plant.

  7. Donna P May 7, 2009 at 10:45 am #

    Hi Mark, We have taken your advice from last year and treated our 1/2 acre pond every 2 weeks with bacteria and pond dyes. It did seem to help. However this year the algae is much heavier, and I’m sure the cause is the 2 geese that decided to nest on our little island. 3 days ago they hatched 3 little goslings. We’re not passionate about Canada geese, but we do love and respect wildlife, so they are here for the summer and the poop is only going to increase. I do not want to use algaecide, but should I step up the frequency and quantity of bacteria that I am currently using? Any other suggestions?

  8. g35lady May 7, 2009 at 12:18 pm #

    Does pond salt help with the algae at all? Two years ago when we put a new liner in our pond, I added pond salt to the water, as recommended by our pet store. Do I need to add more salt this year?

  9. lsdfj May 7, 2009 at 12:48 pm #

    We have a large (5 acres)and deep (40′) pond holding about 35m gallons. Your website would be more useful if it addressed problems associated with ponds of this size. In particular, we have problems with turbidity and geese waste.

    Please address ponds of this size from time to time.

  10. Mark May 7, 2009 at 1:22 pm #

    Hi Donna,
    Geese can certainly increase the nutrients in a pond, as can any waterfowl. Are they the primary factor though…it’s hard to say but I would also look for other things that might be helping. If you have used beneficial bacteria before and the pond and algae responded favorably to it, then I would try perhaps increasing the dosage to see if it helps. Often it can.

    The thing with bacteria, in my experience, is that you not only treat the pond for it’s size (that would be the minimum dosage I would use) but also you must treat to offset the nutrient influences. With this in mind, I’ve ended up sometimes doubling the recommended amount based on pond size only, just to offset the influences of a lot of decaying leaves at the bottom of an algae infested pond.

    So it’s worth a try to adjust the dosage. Give it a month or two at a higher level and see if the pond responds to it. It very well could.

    Hi g35lady…
    Usually salt is added to help with fish health more than anything else. I don’t consider myself a fish expert at all, but do know that it helps them with their slime coating and overall health. It certainly doesn’t hurt anything to add some pond salt from time to time and if it helps the chemistry of the pond or limiting algae growth, all the better. I don’t believe though that salt could be considered a primary treatment for an algae problem. Some form of beneficial bacteria would likely do far more good in that regard.

    Hi lsdfj…
    Thank you for your comments. It’s a challenge to be all things for all people and ponds but we do try. One thing I’ll mention regarding larger ponds…our treatment suggestions don’t change that much based on pond size necessarily. High nutrients are still the main issue but for large ponds, the cause is generally more environmental, rather that something like fish loads that is a common issue in a small pond.

    There is also the practicality of affording the treatment of a larger pond. At some point, some respect to a budget must be given and with that in mind, we often recommend looking at more mechanical options to help with larger ponds. As I often say, additives..add up…and while you may need and want to use something like bacteria for a time to help balance the pond out again, it’s best to use this in a very supplemental way and rely on cost effective mechanical solutions for long term cleansing. These would include aeration systems if there is adequate depth for them (over 10 feet) or ultrasound, which is proving to be a very good way to treat large bodies of water.

  11. Ron May 7, 2009 at 4:27 pm #

    I have found your info quite helpful..
    I will tell you : Barley pellets from the local
    pet store has controlled my algae problem for years.
    It’s natural and does not harm my fish at all.
    The key is : get it in the pond biofalls as early
    as you can in the season and then add more mid-summer.
    trust me I’m as cheap as cheap comes and this stuff is cheap cheap cheap BUT It works great.
    I would not use anything else.

  12. Kathleen May 7, 2009 at 7:50 pm #

    Hi Mark,

    I have a question concerning my bio-filter (I bought it upon your advice, thank you). It has the little plastic spheres in it. Do I need to add the beneficial bacteria or do they build up by themselves? and if so, do I add it to the filter itself where the balls are or in the pond water. My bio-filter did not have any instructions with it at all.


  13. Mark May 7, 2009 at 8:48 pm #

    Hi Ron…
    I totally agree. Barley in any form, may or may not work for a pond algae problem but when it works it sure is a good solution.

    What’s interesting to me is that several universities studied barley and had really mixed results and I wouldn’t call their results “glowing” but we have a lot of customers who use bales, pellets, and concentrate so it obviously works for many people, just as your post indicates. Well done on your end!

    Hi Kathleen…
    It really depends on what bio-filter you bought. Some of them, like the aqua ultraviolet filters we carry, come pre-charged with bacteria in the media. For many others you’d want to add that to the pond or to the filter and get some colonized bacteria going in the filter itself. I would suggest, just in case that you do the latter and supplement for a time with some bacteria, it’s pretty affordable to do that and then you know for certain that you’ve got things balancing out.

    Remember, it can take a few weeks to get things really established in the filter. Once you do though, you shouldn’t have to do too much to keep it up and running well.

  14. Shilah May 9, 2009 at 6:19 am #

    I’m kind of at a loss. Last year we had a big problem with string algae in our 5,550 gal pond. Last month I drained the pond to about 18″ (from 4′) and scrubbed the liner as much as I could. It sat at that low level for about 2 weeks, until I could get my water lilies replanted and set back in the pond. We filled it back up 2 weeks ago, put in a new AquaSphere, new filters, bacterial gel, barley straw extract, and pond dye. The string algae is already growing back, and it’s not even warm yet. I don’t know what else I could have done, and fear we’re going to have another problem this year. There is no environmental problem around the pond. We do have hard water, and I don’t know if this has anything at all to do with it. Any suggestions?

  15. Shilah May 9, 2009 at 11:34 pm #

    The rest of the story!… I took my push broom and brushed down the sides of the pond today. It turns out that the algae was not actually adhered to the liner, it had just settled on it and brushed right off. I’m thinking that when the pond was dry, the stuff I couldn’t get off dried up, and when I refilled it, it fell of and was floating around until it settled. So I feel like there’s still hope. I will say, I don’t care much for the blue dye, and I only used about 1 oz. in 5,550 gallons. I know it’s supposed to shade the water, but with the black liner it looks more green than blue, and I can’t see my fish as well. Oh well, it’s better than algae, and I hope it will be better this year than last year. When my pond water was low, I did scoop about 2″ of sludge off the bottom, from decomposing leaves from the year before last, which I’m sure was alot of the problem last year. There’s so much to learn…so share your discoveries with all of us!

  16. Linn May 11, 2009 at 3:29 pm #

    I see good questions but where do I find the answers. I am having the same problems with sting algea.

  17. Mark May 11, 2009 at 4:32 pm #

    Hi Linn,
    The answers to your situation can vary which is why perhaps nothing is standing out as the solution for you.

    String algae, at least in my mind, is no different that most other algaes. It needs nutrients to survive and those come directly from the water. Lowering them will help keep string algae under control.

    This article and some of the comments discuss some of the problems as to why you might have algae in the first place. Address these and you have the answer.

    I wish I could tell you there was a single, silver-bullet solution to every algae issue, but that would’nt be the truth.

    If your pond is smaller I almost always suggest adding beneficial or desirable plants, and beneficial bacteria. Ours is called the Algae Solution and you can find it on this site through the links on the left hand side of the page…but there are many brands and options.

    These two things, plants and bacteria, work very well together and are very safe for fish and pets, which is a concern for many people.

    I should note though, that as good as these steps might be for the pond, if you have too many fish in a pond for it’s size, or poor filtration, or any other major imbalances, then most “treatment” protocols won’t work until the underlying problem is addressed…which is really the major point of this article.

    For additional information, you might read or re-read our Five Days To A Healthy Pond Report. Most folks on our mailing list have already read it but I’ll post the link again just in case. You can find the report through the link below.

    I hope this helps a bit.

  18. sdstohler May 12, 2009 at 9:50 am #

    Hi Mark,

    I am havimg an alge problem for the first time mostly because its the first year for a full pond. we spent most of lsat summer waiting for it to fill. my question is . is there a formula to determine how wide my outlet must be to my biofilter to flow about 10,000 gph thru the filter? I can make the filter as big as 30′ X 100′ and the pond is an acre median depth 5-6 and 9′ at deep end. I would really like th flow 60,000 gph and make a river water feature at the upper end of the pond. thanks for the site Scott

  19. Shilah May 14, 2009 at 3:55 am #

    Reading an article on barley straw pellets, it said that a peat bottom is good for clear water. My water is very clear, and there’s a layer of loose algae that settled on the bottom of the pond. Is that what they mean by a peat bottom? I will be adding barley straw pellets to our pond as a regular additive, but I’m wondering if I’m using too many products. I use the AquaSphere, and have innoculated by filters with bacterial gel. Would barley straw pellets compliment these, or is it too much? If not, how much should I used in 5,500 gallons, and how often should I replenish them?

  20. Mark May 18, 2009 at 5:19 pm #

    Hi Shilah,
    Regarding your question on the products. All of these that you mentioned don’t conflict with one another, which is probably the main thing that could come up. Barley and bacteria work in different ways and both can help in certain situations.

    The one thing I caution against in using too many products, particularly early on in treating an algae issue is that you don’t always know what’s actually working. If they all work together and get the job done, that’s fine, but ideally to save on costs, you want to try one product at a time and narrow things down to what works. If you find something partially effective, then add something else for a time to see if it helps a bit more.

    Many algae issues do require more than one type of treatment or protocol to totally control it. Some of course, only need one thing to really fix the problem, but the stubborn issues, might need a few different approaches over time.

    Testing things one by one, then combining when it seems practical to try is probably the best way to go forward.

  21. Shilah May 28, 2009 at 7:55 pm #

    I am still wondering what a peat bottom means. Like I said in my May 14 post, I have loose algae that has settled to the bottom of the pond, and is also on the sides. If I stir it up, it’s all loose and clouds up the water, then it settles back down onto the lining. Is this good or bad? I have added barley straw pellets, and a new Aquasphere, and am waiting to see if anything changes. What I’m wondering is if this loose algae is normal, or if it should go away. I don’t want to wait until I have string algae growing again to make that call.

  22. nancy June 1, 2009 at 4:02 pm #

    i have been having a terrible time with algae my water is always green. i am wondering if i don’t have a good enough fitration system. i have the aquascape filter – filter pads and lava rock with the skimmer – it has a filter pad and net.
    also this year i tried a pool filter and am backwashing it. i also add the biosphere pro every month for under 25,000 gallons. this just does not clear it up. my pond sits in the sun and i have lily pads and a few other plants. pond is about 25 x 30 – 2 feet deep
    i have about 20 fish. i am going to try barley and see if this helps any.
    any suggestions would be helpful.

  23. Mark June 2, 2009 at 9:53 pm #

    Hi Nancy,
    It’s possible you could be underfiltered but I might also suggest adding more plants if your comfortable doing that. The sun really can create a green water condition pretty easily which is why floating plants are so beneficial to helping balance a pond out. That and adequate filtration can often be enough. I like barley products. They do not always work of course but they are worth a try in my opinion and many folks swear by the stuff so it does work in a number of cases to control algae.

  24. Shilah July 28, 2009 at 2:48 am #

    Well…same algae problem I had last year. My water looks OK, but my liner is covered with green fuzz, and string algae growing along the top few inches of liner. The algae seems the thickest and healthiest where the water is running the most…waterfalls, stream bed, over the aerators. I have a bag of barley straw pellets under one small fall, and there’s algae growing on the bag! My pond is 5500 gallons with only 9- 6″fish, 25 water lilies and misc other plants (not too many) I do have alot of sun exposure, but the problem was already starting before it got hot. I had another layer of muck on the bottom a month after I cleaned it out, and I cleaned it out again. I do have hard water, but everything else tests out OK. I’m considering a smaller preformed pond to move my fish and plants to, and chlorinating the heck out of the big pond and using it for a swimming pool. I feel like I’ve done pretty much everything right, with no success. I wish an expert could look at my pond and tell my why I’m having so much trouble. I don’t know what else I can do.

  25. Bob and Pat Mills November 18, 2014 at 12:21 pm #

    Our big secret to pond algae is that the 5 acre pond is surrounded by trees and farmland that drains into it. The pond is around 50/60 years old and there is nothing we can do about it, as far as I know. The filamentous algae, duckweed and watermeal are the biggest problems. A neighbor is going to treat with sonar in the spring. We had a major, major fish kill last summer. I think I wrote you about it. I’ve contacted so may pond experts that I lose track. We also had a tornado hit last year and have a lot of tree trash & a few trees in it.

  26. Mark November 20, 2014 at 4:13 pm #

    Hi Bob and Pat…thanks for the comment. I’m sure if you and I visited on this we would have covered having good aeration in the pond for starters and then you’d need to reduce nutrients using some form of beneficial bacteria. That’s about the only way to clean this type of debris up in any reasonable manner. In truth though, for a 5 acre pond, it would require a bit of an ongoing investment that not everyone can make. So you have to pick your battles as you’re discussing with Sonar. But that probably won’t help with some of these issues and once your remove the duckweed / watermeal you can bet that algae will come up stronger and you’d need to treat that as well. I would forecast a bit of an ongoing battle here but it may be the only thing you can do if you’re unable to work on the problems with good bacteria. As for the fish, aeration is the only tool that will help when weather conditions get extreme.

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