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Thread: Redfield Ratio - A way to control algae?

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    Redfield Ratio - A way to control algae?

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    Just found something on the web. There is a school of thought and followers that beleive an important aspect of algae control is to get the right Nitrogen to Phosphorus ratio. Check out the below article.
    http://www.xs4all.nl/~buddendo/index.html

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    I don't really believe in it at all. Planted tanks does not require that narrow of a range to work well. As long as the nutrients don't get bottom out from plant uptake and yet limited within a boundary by large water changes, things would go very well. That is what I believe...it works. I have no algae.

    Regards
    Peter Gwee :wink:

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    Hi,

    The ratio applies where these are limiting, if there's an ample supply
    relative to light/CO2, then the ratio does not matter.

    You can have 2 ppm of PO4 and 2 ppm of NO3 as long as this ratio and
    levels are stable, it works fine as does 20ppm of NO3 and 0.2ppm of
    PO4.

    The ratio also includes NH4, which will make a huge difference if a
    large fraction of the N is NH4(algae will grow). There are organic
    fractions which the plants generally cannot use, a similar situation
    occurs with PO4. Algae can use these organic fractions, unlike the
    plants. These differences are significant when talking about plants
    and algae and dominance in your tank.
    Regular large water changes will keep the levels of the organic
    fractions down.

    In a high light tank you might have to dose more frequently to keep
    this ratio but this whole mess with ratios does not limit algae in and
    of it's self nor is it that horticulturally important.

    As long as the growth needs of the plant are available, then the ratio
    can be quite high or low. These are generalized ratios, specific algae
    and plants can vary widely.

    FW algae have ratios of 14:1 and FW macrophytes have about a 10:1 N:P
    ratio.
    Redfield's ratio is based on marine algae, not FW macrophytes or FW
    algae.

    We are trying to grow the macrophytes/plants are we not?
    Shouldn't their needs be addressed since that is what we are selecting
    to grow? I can also assure you that FW algae can and do grow nicely at
    16:1 ratios N:P in many aquariums.

    It seems to me if you base this arguement solely on the ratio, 16:1
    would favor the algae, not the plants with their richer P content
    relative to N.
    There's talk about algae's ratio but not the plants which is the focus
    of a planted tank.

    10:1 ratios are generally mentioned as best for submersed aquatic
    plants plants, but this will mainly save you a little KH2PO4 and KNO3
    as you do a water changes to prevent any build up or depletion. These
    are quite cheap. So as long as all the plants have either, then the
    plants grow great and there's little algae presence.

    A simple way to maintain a ratio: Do large weekly water changes(50+%)
    to prevent any nutrient build up, dose frequently to prevent anything
    from running out.

    Good plant growth is the key. That is how you outwit algae. That is
    the best path IME.

    Regards,
    Tom Barr
    That will explain pretty well....

    Regards
    Peter Gwee :wink:

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    Peter,

    Thank you for copying Tom Barr's reply here. I appreciate that.

    Yes, it is clear that keeping nutrients and other parameters in sufficient levels are basic of plant keeping. However, I think one good practice in the Redfield's method in that PO4 is kept in low level in water column.

    As I shared with you that I am into "no water change" (I only siphon debris during pruning) for the past few months. For this method, I find keeping PO4 in low is essential; to counter that low level, I inject PO4 into the substrate. You should try the "no water change" as it is the effective way to bring up skill level in handling planted tank.

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    Sorry freddy, I'm just not into your no water change method. The potential of nutrient buildup is pretty great imo as plant uptake is different from day to day and the fact that the dosing regime I am employing is by means of dosing in excess to prevent the risk of limitation. (NO3 and Cu buildup is the main problem..)

    By the way, how much light do you have over your tank? Dosing regime? Plant load?

    Regards
    Peter Gwee :wink:

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