Which NO3 Testing Kit is best??

Discussion in 'Water Chemistry' started by REDSTEVEO, 12 Sep 2016.

  1. kadoxu

    kadoxu Member

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    It does makes sense... but you start by saying the end result, which makes it more confusing.

    So you have 5ml of water reading something above 40mg/l.
    You add 5ml of de-ionized water, meaning you now have the same amount of NO3 in twice the water volume (10ml).
    If you can read something bellow 40mg/l, let's say 25mg/l, in 10ml of water, it means you originally had 50mg/l of NO3 (=25x2) in 5ml of water.

    If, on the other hand you still read 40mg/l, you have to repeat the process, adjusting the math.
     
  2. dw1305

    dw1305 Expert

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    Hi all,
    When the test measures in elemental nitrogen (N) it will give you a much smaller number than if it measures NO3.

    The RAM of N = 14, and O = 16. In NO3 you have a RMM of 14 + (3*16) = 14 + 48 = 62. So this where the "14" and "62" come from.

    So NO3 is 14/62 ~ 22.6% N.

    If you divide your 5 ppm N by 0.226, it gives you 22.14 ppm NO3.

    You don't really need the maths, if you multiply the N value by 4.5 you are pretty near the NO3 value (22.5 ppm).
    When you have a sample that reads above your highest standard (in this case you don't have to create a calibration curve, Hach have already done it), you need to dilute that sample so that the value lies on your calibration curve. Because you've doubled the sample volume with DI water (which doesn't contain any NO3) you need to double the recorded value (37.5 * 2 = 75)

    Curve is actually a bit of a misnomer, because ideally you want to read the sample value near the origin of the curve, in the initial linear section.

    This is one of the problems, if you did as suggested your value (right at the top of the curve) would probably still be an underestimate of the true NO3 value. You can carry on dividing your sample by 2 with DI water (1:2,1:4 (multiply value by 4),1:8 (multiply by 8)) until you get a repeatable value, but in the case of off the scale nitrogen a 1:10 dilution (1 part tank water, 9 parts DI water) would be more likely to give a more accurate result.

    The question really has to be is this process likely to give a better estimation of NO3 values than visual estimation of nitrate provided by the "Duckweed Index" and a conductivity reading? For me the answer is probably not.

    I get quite a few PM's on other forums that start with a statement like,
    and I tell them to trust the plants.

    cheers Darrel
     
  3. REDSTEVEO

    REDSTEVEO Member

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    So err...this Duckweed Index...just chuck a bunch of Duckweed in the top of the tank, if it turns yellow, then low levels of NO3, if it stays dark green and spreads like wildfire, then NO3 levels too high right...:confused:

    Just read other articles re 'High Nitrate Levels' and saw the difference between Organic and Inorganic NO3. The stuff we add as part of EI is Inorganic, so not harmful, or at least not as much as Organic caused by poor filtration, over feeding, overstocking and poor water maintenance.

    What type of Duckweed are we talking about here?
     
  4. dw1305

    dw1305 Expert

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    Hi all,
    <"Yes">. It doesn't sound as accurate as looking at changing colours on a test kits, but really it is the same approach, but just much more robust.
    The <"Lemna bioassay"> is widely used in waste water treatment, and <"phytoremediation"> with floating plants is used to clean up all sorts of polluted wastes. The problems with Lemna were that it doesn't like very soft water, it needs reasonably high levels of nutrients and it is a PITA to harvest. After some experimentation I found that there was a "Duckweed" that didn't have these limitations, and it was Amazon Frogbit (Limnobium laevigatum).
    I subsequently bought a copy of <"The Optimum Aquarium">, to find that the authors had used a similar approach to the Duckweed Index in the 1980's.

    Because plants needs about x10 the amount of nitrogen (N) and potassium (K) compared to phosphorus (P), (and x3 times more phosphorus than any of the other elements) deficiencies are most likely to be nitrogen or potassium. Other options that cause chlorosis are magnesium (in older leaves) and iron (in younger leaves). Nitrogen and potassium deficiencies show up in old foliage first, and both cause yellowing (chlorosis) and smaller leaves.

    Floating plants aren't CO2 limited and show a really quick greening, and growth response, to added nitrogen. If you add nitrogen, and your plants green, they were nitrogen deficient, if your plants are a large, lush dark green they have plenty of nitrogen. When you harvest a plant you remove nitrogen (largely incorporated into the photosynthetic proteins) from the tank.

    cheers Darrel
     
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  5. dw1305

    dw1305 Expert

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    Hi all,
    Pretty much, usually in aquariums (and eutrophic rivers etc.) nitrate is the final product from the oxidation of ammonia, the NO3 itself isn't toxic until you reach significant levels. Fixed nitrogen (nitrogen that organisms can utilise) is a scarce resource, so in nearly all natural situations it never accumulates, so when you have a lot of it it is a marker of pollution.

    In non-planted aquariums high levels of NO3 indicate that you aren't doing enough water changes, because NO3 is only removed by anaerobic denitrification and/or water changes.

    Planted aquariums are different, because the plants directly take up both NH3 and NO3, and are net oxygen producers. High levels of dissolved oxygen mean more efficient biological filtration and efficient biological filters are "nitrate factories".

    We need to add nitrogen to heavily planted tanks because nitrate levels fall over time, rather than rising. If we don't add any nitrate, plant growth will slow as nitrate levels fall. I still have water changes, but I only change a small volume of water ~10% ~every day.

    I keep Apistogramma, which come from similar water conditions to Discus, and I use a combination of Duckweed Index feeding and conductivity measurement for tank management.

    cheers Darrel
     
  6. Paulwilsonwhite

    Paulwilsonwhite Newly Registered

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    Hi.
    I find this information very helpful and another way of keeping your tank healthy.
    I will just digest what I’ve read and put together some questions because this is truly interesting
    Cheers Paul
     

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