Faden algen - rapid growing

  • Hello everybody here at the forum.

    We build our 250m2 schwimmteich in 2015 with help and products from Glenk here at TopTeich.

    The first years we had clean water and almost no algea growth.

    2017 was different - we still had crystal clear water -but the algeas was growing and growing and growing.

    We kept harvesting loads of faden-algen but a few days later we could start over again. Reason? I don't know.

    This year is starting to be the same as 2017.

    The water is clear, but algeas keep growing -very fast and continuously.

    We have a phosphat measuring device and it shows a value between 0 and 1 ppb -which means almost no phosphat for the algeas to grow of.

    But why do the algeas keep on growing? What do they live of and what can we do?

    Could it be a high level of Nitrat?

    If so - what to do?

    The water is 100% clean and fresh and visibility is several meters.

    But working 10 hours per. week harvesting algeas is not fun.

    All cirkulation in the pumps, hoses etc. is good and running. You can see our lake in my profile here at the forum.

    Please do not hesitate to ask further questions!

    We hope that some of you can point us in the right direction - we thank you so much!

    Greetings from Denmark

    Jens Christian Nørtoft Bækgaard

  • Hello again - I just did a re-check of the phosphat level.

    First check on lake water = 0,001 mg/l P (= 1/10 of the normal 0,01 limit)

    Next a check on our "city water" from the water tap: reading of 0,054 mg/l P (=over 5 times the 0,01 limit)

    Second check on lake water = 0,000 mg/l P (= ...well no phosphat!)

    Still we have day to day visual big growth of faden algen!!

    What should we look for??

    Please help -thanks :)

    Best regards

    Jens Christian

  • Hi Kotzbrocken - thank you for answering! :)

    We have a Tapir 12000 and it runs for about 10minutes drawing dirty water out the filter gravel-layer each spring.

    After 10 minuttes the water comming out is clear and we start the normal pump cirkulation.

    For long I have focused on the phosphate level - we also put in a phosphat binder block.

    But as mentioned: the phophate level is double measured to almost "0" -so I am looking for other reasons now.

    I can only measure the phosphate level my self. But I will have a water test done to check for Nitrate etc.

    I think that will be the best next step.

    Do you agree?

    Thanks again!

    Best regards

    Jens Christian

  • Hello again

    I will try to describe our conclusions and hopefully some of you can answer our questions in the end :)

    Our suspicion is that the gravel layer is the source of energy/phosphat to our algea growth.

    I am not sure of the actual bacterial processes that goes on in the gravel layers. But as I understand the process the bacterial cultures transform the phosphat (and other) to harmless minerals etc.

    But what happens to these minerals etc?

    Is our gravel layer "full" and there fore now slowly leads the phosphat back to the water as it flows through the gravel layer?

    A phosphat reading in our filter-boxes (just before the water is pumped out into the gravel layer) is significantly lower than a phosphat reading taken just above the gravel layer (where the algeas grow).

    That leads us to believe that the gravel layer is "leaking" phosphat back to the water.

    As Mr. Kotzbrocken wrote earlier - our reverse cycling of water at spring startup might not be sufficient.

    To save water I only pump untill the water comming from the pump is clean by the look.

    That is about 10min. = 2 m3 of water.

    Our teich is 250 m3 of water and approx. 60 m3 of cleaning gravel layer.

    Could it be that simple - we do not reverse cycle enough?

    If so:

    a) what would be a reasonable volume of water to reverse pump through the gravel layers?

    b) would it make sense to make a better reverse pumping session now -or it is too late now?

    Please ask all the questions you have and let us know your input on the questions above.

    (We still have 100% clear (and warm) water and enjoy our teich very much! )

    Thanks in advance -and greetings from Denmark.

    Jens Christian

  • Hej Jens, hvor langt op i Danmark bor i ?

    Kunne godt taenke mig at besoege hjer engang ( hvis det passer ) og kigge paa hjeres soe :)

    Vi bor lige syd for graensen i retning af Kappeln.

    Hilsen fra Jens :)

  • Hej Woodfriend :)

    I er meget velkomne!!

    Vi bor uden for byen Vidlbjerg, som ligger mellem Herning og Holstebro i Midtjylland.

    2 - 2,5 times kørsel fra grænsen.

    Skriv en sms til mig, så får du vores adresse osv :)

    Mobil: +45 26853375

    I dag søndag har vi huset (og søen) fuld af gæster, så jeg svarer nok ikke før imorgen. Men skriv endelig!

    Mvh og god søndag

    Jens Christian

  • Hi Jens Christian:

    Regarding Phosphate measuring: Which kind of device/assay do you use?

    There are not many assays on the market that are reliable at the low concentrations of ~ 0,001 mg/l ortho-phosphate that are required in swimming ponds.

    Phosphate adsorption: As I understood, you don't have any plants in the pond for phosphate elimination? Only gravel as biofilter for microbial phosphate binding?

    My personal experience: Emerse plants are much more efficient in phospate absorption than bacterial biofilters. You should think about a regeneration zone with plants!

    Gravel: Did you check you gravel for phosphate content? It is not very likely for your gravel, but many types of stone release phosphate

    There is often considerable phosphate input from atmospheric sources. In your case, there is probably substantial input in the dry summer months due to wind erosion from the neighbouring field. You should consider that! Again, the best way to prevent algae growth is dense planting of emerse plants in a regeneration zone tha absorb the phosphate. I autumn you have to cut the plants in order to remove surplus phosphate from the pond.

    Nitrate: Nitrate should not be the reason for algae growth.

    In fact, meanwhile many swimming ponds are meanwhile fertilized with some nitrogen during the growth season to enable lush growth of plants. In addition, also sufficient macronutrients (Potassium, Magnesium, Calcium, Sulfate) should be available (you should check for). Moreover, all necessary micronutrients have to be available for good plant growths.

    If you have a dense planting and good plant growths you will not have algae problems anymore.

  • Hello Usipp - thank you for your reply - I have not been on the site for some time, so I did not see it before :)

    You could be right about the plants. For now we have only a few plants to make the lake nice to look at.

    This year we did the rückspülen much longer than we have the past years as suggested. But still the algea growth is high in the gravel areas. It still seems that the gravel layer is slowly but ongoing releasing small amounts of phosphat that keeps the algea growing in the regeneration zone.
    Water is 100% clear.

    So more or less the same picture as last year.

    One thing I would like your answers for:

    Our lake is about 250m2 and holds about 250m3 of water, 60m3 of cleaning gravel in about 120m2.
    The gravel/cleaning zone is supplied with water through 3 x "drainstar". So each drainstar covers about 40m2 of the gravel/cleaning zone.

    When rückspülen with our Tapir 12000 - I tried to block two of the drainstars off and run the 12.000ltr/hr pump in each section at a time.

    But I had to give up on that - and so we reverse pumped the complete 120m2 simultaneausly.

    We pumped out about 30m3 of water.

    My concern and question:

    Is the flow through the gravel layer with the Tapir 12.000 high enough to release the build up in the gravel?
    If I could block off 2 out of 3 drainstars the actual flow would be 3 times as high pr. m3 gravel.

    Could this be the problem?

    Should we try to stop the pumps for 2-3 weeks and reverse pump again -this time one drainstar at a time?

    I hope that you have som input - we love our lake, but the thought of having to "harvest" algea week after week makes me very tired and sad.

    Thanks in advance - and please ask all the questions you might have.

    Best regards and greetings from Denmark
    Jens Christian Nørtoft Bækgaard

  • Hello again.

    What kind of pumps do you use when rückspülen?

    I have the book "Schwimmteich Planungshilfe" by Ralf Glenk and had Peter Latzel as "teacher" when we build our schwimmteich.

    In the book there is a chart showing that with f.ex. 40m2 of filterbereich a pump power of up to 4.000l/hour is good for Phosphatreduction, from 4.000-20.000l/hour is good for partikel- und nährstoffreduction. And finally that to "rückspülen" you need a pump that moves from 20.000 - 40.000 l/hour.

    That is for 40m2 filterbereich - we have 120m2....

    As mentioned above - we would be able to block off 2/3 of the filterbereich and only do rückspülen in 40m2 at a time.

    But still - how do you produce a suction power of between 20.000 and 40.000l/hour?? That is a lot!

    My Tapir is a 12.000l/hour pump -I need 2-3 times that...!

    So again: What kind of pumps do you use for rückspülen?

    I am convinced that a thourough rückspülen is what we need to help our situation (read above).

    Please let me know your thoughts and advice...

    Thanks from Denmark
    Jens Christian Nørtoft Bækgaard

  • Hello Ralf - thank you so much for replying! :)

    You write that the power of the pump does not matter - but according to page 92 in your book the pump should be powerfull to make a "rückspülen" ...

    Earlier years I only ran the Tapir 12000 for a few minutes untill I could see that the water running out was clear (to save water) - that was obviously wrong.

    But this year we ran the pump for hours -pumping out 30m3 of water through the gravel layers.

    ..but still we have strong algea growth in the gravel layers, just as last year.

    That is why I thought that maybe the flow of the water during the "rückspülen" was not strong enough to free the nutrients from the gravel.

    The water is 100% clear -but it seems that the gravel layer is slowly releasing phosphat etc. to feed the algeas...

    What do you think?

    Should we look in a different direction for a solution?

    Thank you very much for your help!

    Best regards

    Jens Christian, Denmark

  • Thanks again: the gravel is heat treated quarts gravel - that should be the cleanest possible and no phosphate.

    The layer below the filter gravel where the water is distributed evenly under the filter gravel (and the edges) are of bigger washed gravel from the north sea.

    The bigger gravel could be "leaking" phosphate.

    But can that match the fact that the first two years we had absolutely no algea growth - but we have now.


    • Offizieller Beitrag


    Mince a small amount of gravel and pack it with pond water into a glass. For reference, a glass only with pond water and another with refill water. If the gravel releases phosphate, you should see a stronger algae formation on the first glass. is worth a try without much effort.

    hope the english is readable ?‍♂️

  • It is absolutely - thanks :)

    I will give it a try.

    When we made the lake -we made that test with the gravel in a water sample and had it sent of to test.

    It did not show any phosphate release. So I do not suspect the gravel it self.

    But I will make the test with the gravel as it is today - presumably containing lots of nutrients.


    Jens Christian

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