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A question about inhibiting algae growth

Discussion in 'General Plant Topics' started by Carissa, Oct 24, 2007.

  1. Carissa

    Carissa Guru Class Expert

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    This question has been percolating in my mind for a while. So it's time I just ask it.

    People say that if you have healthy plants, they outcompete algae. I have found this to be the case in practice, when my plants are growing well, I have few if any algae issues. When I'm not fertilizing properly etc. algae issues abound.

    Ok now here's the thing. The idea that was put forth to me (that maybe isn't true) is that plants suck up the nutrients in the water faster than the algae can use them, hence "outcompeting" it. But this doesn't sound right. In a tank that you are dosing EI in, the goal is to ALWAYS have more nutrients than the plants can use up in the water column. So how are the plants outcompeting the algae? Outcompeting for what??

    Then there's the light issue. Lets say that you have two tanks that have identical water conditions (fertilized), and both have high light and co2 injection. But one has plants, the other doesn't. What would you see as far as algae goes? I've never tried it, but I have been led to believe that the one without plants would have lots of algae, and the one with plants would not. But why? Don't algae in both tanks have access to the same exact nutrients?
     
  2. nwfishinfool

    nwfishinfool Prolific Poster

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    Carissa,

    I'm so glad you took the time to ask the question and I really look forward to the answers. I too have wondered the same thing!
     
  3. Tom Barr

    Tom Barr Founder
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    Carissa,

    Yes, all good common sense questions.
    Based on those observations, what things might be going on?
    You know it's not due to, NO3, PO4, K, Fe etc, but what about NH4?
    What about allelopathic chemicals given off by plants?
    What about poor CO2 levels?

    How might you test and investigate those issues?

    Regards,
    tom Barr
     
  4. swylie

    swylie Prolific Poster

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    Carissa, I think the experiment you propose is a good one.

    Intuition and logic suggests to me that the idea of "outcompetition" is more complicated than most people are led to believe, and is probably different for each nutrient depending on concentration and location in the tank. Light competition is obvious because we can see it with our eyes. Are NO3 or NH4 concentrations the same in all regions of the tank, though? It's hard to say. Even harder if you're talking about algae growing on the surface of a leaf, and you're interested in nutrient concentrations on the algal surface and on the leaf surface.

    I think the idea that healthy plants outcompete algae is BS though, as long as you're maintaining nonzero nutrient concentrations and not talking about spatial competition, like for light. In general, algae and plants will have access to the same levels of nutrients. Following the EI theory, algae has constant access to nutrients. Where's the competition there? In my mental model, I'm just not seeing it.

    Tanks which maintain a near-zero concentration of any nutrient are different, of course.
     
  5. Carissa

    Carissa Guru Class Expert

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    It seems obvious that there is something different about the water in highly planted tanks as opposed to non-planted tanks, something that either stops or encourages algae.

    One thing here that may answer my question partially and that I hadn't thought of...NH4.

    My understanding and intuition about what would happen is based on tanks WITH fish. I could start with a hypothesis that fewer plants in a tank with fish means higher concentrations of NH4...which leads to algae in tanks with fewer plants to process the NH4 quickly.

    To test it I would have to have two tanks or to do it justice three or four....two tanks without NH4 addition and two with. One each non-planted, one each planted. Then see where algae starts happening first.

    If it's NH4...you'll see it the worst in the non-planted NH4 tank....secondary to the NH4 planted tank....the other two should be significantly less. If it's allelopathic chemicals....you'll see the concentrations in the non-planted tanks as opposed to the planted tanks.

    Now if I only had four tanks....
     
  6. Tom Barr

    Tom Barr Founder
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    Think about his:

    Add NH4 to a planted tank with high light(this reduces the time required to see algae)

    Kill the Gw bloom with a UV for 2-3 days.
    Wait 1 week to see if any regrowth occurs.

    If not, try adding high NO3.


    Any response?
    If not, then add NH4 and see.

    If you do this several times back and forth, without fish, then you can know it's NH4.

    Next you add fish, or shrimp back.
    Then you keep adding progressively more and more until.......you get GW.
    You can test, but the NH4 is used up pretty fast.

    you can do large water changes to remove excess NH4 also.
    so myou can dose NH4

    Now you do this a few times till you convince yourself that NH4 can cause algae.
    What about low light?

    Probably, but it does take longer and who knows what occurs during that time. Messing with CO2 also changes the NH4 uptake rate by plants.
    Plants stop growing, stop producing O2 and bacteria and fish have less O2.
     
  7. VaughnH

    VaughnH Lifetime Charter Member
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    If you removed all of the algae from a badly infested tank, dried it and weighed it, I'll bet you would have a very small number compared to if you did the same with the plants. That dry mass is made up of the nutrients the algae/plants consumed. That makes me believe that algae require far, far less nutrients than plants do to grow well. And, if that is true, then algae couldn't possibly out compete plants for nutrients, and they wouldn't need to - table scraps would suffice for algae.

    So, the only real competetion is for light. When algae covers a leaf, it starves that leaf of light. When green water is going strong the algae is getting a lions share of the light. But, when the plants have grown well, and are up near the top of the tank, they take away light the algae could use.

    Since algae just don't have the mass to out compete plants even for ammonia (nitrogen), the ammonia-as-a-nutrient question can't be a competition either. But, if algae look for ammonia as a sign that growing conditions are good, then the plants, by using up the small amounts of ammonia always being generated in the tank, prevent the algae from getting the sign.

    That is a simplistic, non scientific way to look at it, but I can understand it that way.
     
  8. Carissa

    Carissa Guru Class Expert

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    Yeah, this is exactly what I meant. I don't think algae need easily detectable amounts of ammonia to tell it to start growing. But when plants start getting deficient, I'm thinking maybe then they can't use up the ammonia as fast as they could before. Then that somehow tells algae to start growing. When it grows on the plants it kills them, causing ammonia levels to rise further, etc. until algae reign. But maybe if new, healthy plants were introduced into the system, or the source of ammonia was removed, the algae would stop.

    One thing I observed on my tank when it was still cycling backs this up. I was using zeolite which was doing a fine job keeping ammonia at undetctable levels. But suddenly, a fish died. Naturally I immediately checked ammonia. It came back 0. Around the very same time, I started to suddenly notice green spot algae forming on the tank walls for the first time. I didn't put it together until three days later, when I tested ammonia again and found low detctable levels. The zeolite had run out, but the fish and algae knew it before I could detect anything wrong.

    This also would explain why it's good to plant heavy from the start.
     
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