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Are All Nitrates Created Equal?

Discussion in 'Aquatic Plant Fertilization' started by edwardsmith, Apr 25, 2018.

  1. edwardsmith

    edwardsmith Lifetime Members
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    Do plants thrive on all sources of "nitrate"?

    If my nitrate levels begin to get elevated (i.e. 10ppm) but the only sources of nitrates are soil, fish poop and decaying fish food.......are these sources acceptable for plant use?

    Im assuming, nitrate = nitrate, regardless of the source, but wanted to confirm.

    Thinking about adding ferts, but if I already have adequate nitrate, don't want to add more (discus fish).

    Thanks
     
  2. Allwissend

    Allwissend Article Editor
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    Short: Yes, but...
    Long:
    Nitrate(NO3-) is an anion which once dissolved stands surrounded by water molecules. At this point it does not matter if it originated from KNO3, Ca(NO3)2, NH4NO3 or NO2 bacterial conversion. All NO3- will behave in a similar fashion regardless of previous molecule. The nitrate test is not the most precise test when used in actual aquarium samples, but let's say that it will detect NO3 but not be influenced by other forms of N in the aquarium.

    But, not all plant/algae-available nitrogen(N) is nitrate. And here , the intermediary molecules between fish poop and nitrate can affect fish and plants much more than nitrate.

    Hope this answers your question.

    PS. Just to be sure, I am not saying that KNO3 == Ca(NO3)2==NH4NO3. If you think this is what I said, read the post again.
     
    #2 Allwissend, Apr 25, 2018
    Last edited: Apr 25, 2018
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  3. edwardsmith

    edwardsmith Lifetime Members
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    Thanks! I think I go it .

    Based on your explanation, can I have elevated nitrates (10ppm) and possibly still need to add nitrogen fertilizer?
    If I add nitrogen fertilizer, can it increase my nitrates unintentionally?

    I really appreciate the help.
     
  4. Allwissend

    Allwissend Article Editor
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    I would not consider 10mg/L NO3 as high. 40mg/L would be the starting point for high. Ideally you would want levels above 10mg/L NO3 at all times so the plants can grow without issues and maintain their high rate of growth. However, you will find out plants are not going to be constant consumers and they can use 1mg/L in one day and 4mg/L the next day, not only dependent on plant mass. For this reason you will need to add more NO3 than plants need that specific day.

    It is also a problem of concentration, the more concentrated the easier they are to get into the cell. Too concentrated and it is hard to find other things to get into cell or hard to keep them out. Think of it as a bag full of balls(ions, molecules etc.). If you have inside the bag 1 blue ball and 999 yellow balls you will spend considerable more time finding a blue ball than in a bag with 500 blue balls and 500 yellow balls. In freshwater the majority of the balls are just water molecules.

    I would also caution against trusting that 10mg/L NO3 concentration. Test results have a certain degree of uncertainty. If this is not given then you can assume it is very large. The 10mg/L level displayed could be 4 or 24 in reality.

    When you add other sources of nitrogen (available to plants) and it is not consumed by plants it will be converted by bacteria to nitrate. This is basically how fish food increases your nitrates.
     
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  5. edwardsmith

    edwardsmith Lifetime Members
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    Thanks!

    Lol, I also found this from "Plantbrain"......thanks Tom!

    "NO3 or the NH4 loading and the subsequent O2 demand and other waste by products from high feeding rates? If you pack, as most discus folks often do, a lot of large hungry cichilds into a small tank, then over feed them, it's not just discus that will have issues or reduced rates of growth, I'd say all fish would. NO3 from fish waste is an entirely different issue vs NO3 from KNO3.
    One places far more toxic ions into the system and places a larger demand on O2.

    I think the OP might do well to add some K2SO4 and not use the KNO3.
    This should help increase the NH4 and the NO3 uptake by the plants, which in turn will increase O2 and less NH4 will go to bacteria.

    The plants may be limited by K+, Traces, etc, thus not be growing well.
    Healthy plants= healthy fish.

    Improve plant growth= improve fish health."
     
    #5 edwardsmith, Apr 26, 2018
    Last edited: Apr 26, 2018
  6. tiger15

    tiger15 Member

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    I read Tom's article, but don't fully understand.

    I can understand that fish wastes do not provide balanced nutrients for plants, typically lacking sufficient potassium, micros and iron in bio available form. But nitrate is nitrate, regardless of its origin.

    According to Tom, nitrate from KNO3 is immediate and good. Nitrate from fish waste has to transform through intermediary molecules, which is bad.

    It's bad because the process consumes oxygen. Why does it matter if the tank water is adequately circulated to replenish oxygen. If bacteria consumes oxygen, so will they generate CO2 that plants need.

    The intermediary molecules are bad because they fuel algae. Don't plants also uptake intermediary molecules and actually prefer NH3 over NO3.
     
  7. Allwissend

    Allwissend Article Editor
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    Hi Tiger,

    I know you know , but let me first clarify the terminology a bit for other readers/ newcomers.
    NO3- nitrate(plant uptake, limited toxicity)
    NO2-nitrite (some plant uptake, highly toxic)
    NH3- ammonia (plant uptake, highly toxic- even to plants )
    NH4+ - ammonium (form taken by NH3 in acid conditions , the more acidic the higher the % of ammonium, less toxic)
    N2- nitrogen gas (what is in the atmosphere, inert), unavailable to plants, can be used by some specialized bacteria
    N -nitrogen (as in the chemical element)

    Now to address the question. Yes nitrate is nitrate, you will not hear any arguments from me there (when it comes to fertilizers at least). Suppose you had this ideal probe capable of precisely and accurately measuring the NO3 levels in the aquarium. A 30mg/L NO3 reading will mean just that , irrespective of the source.

    The "problem" with biological waste is that you do not have pure NO3 to start. One organic source would be proteins, the decomposition process starts :

    proteins-amino acids - a-b-c-d-e-f-g-h------zzz--NH4-NO2-NO3(-NO2-NO-N2O-N2), where a-z are intermediate molecules and what is in parentheses ( ) is the denitrification part, usually taking place under anoxic conditions

    Fish excrete mostly NH3 and urea, mostly through their gills, so the cycle is a bit simpler for eaten food.

    Every step along the way has by-products and requires the biological activity of bacteria which in turn generate new metabolic products to be processed. Nitrogen is largely unavailable to plants until it reaches the NH3 part.

    Some of the intermediate substances are believed to be signals for algae spore germination

    Conversion does not happen in free water in any significant %, rather it happens in biofilms (substrate, filter, glass, particulate matter in the substrate). As such the oxygen consumption can be problematic creating spots of low O2. If you have a O2 probe you will find that few things reduce the O2 concentration in water more than stirring up mulm in the water column. This is because, processes which were halted due to low O2 quickly take place when exposed to oxygen.

    The same thing can be said about your question regarding NH3 plant uptake, yes plants do take NH3 up when they need it. But there are some hot NH3 spots, the substrate releases some, that uneaten fish food releases some, that dying leave, etc. Plus at some point, plants have their full depending on metabolism, light and other nutrients. This means leftover NH3 for algae.

    Its not possible to stop NH3 to appear in our tanks even in plant-only tanks. This should not be our purpose. However, plant only tanks are so much easier to maintain and have less problems with algae because of the reduced production of organics. Furthermore, if NO3 from fish metabolism tests high what can be said about the un-tested intermediate products. These intermediate products also have an effect on your system and on fish health.

    Hope this helps clarify why inorganic sources of NO3 might be easier/safer to dose in planted tanks.
     
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  8. tiger15

    tiger15 Member

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    So what's really bad is overstocking and overfeeding, because the intermediary molecules generated in the journey to nitrate can fuel algae. A good practice is therefore to avoid over stocking and over feeding, and do regular water change to remove the bad molecules.

    Theoretically, since dosing inorganic nitrate won't remove bad molecules, it has no mitigation effect on algae. In heavy stocked tanks with plenty organic nitrate, dosing inorganic nitrate won't benefit or harm plants because nitrate is the same regardless of origin. So the reason why it’s necessary to dose nitrate in heavy stocked tank remains unclear.
     
    #8 tiger15, Apr 30, 2018
    Last edited: Apr 30, 2018
  9. Allwissend

    Allwissend Article Editor
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    Yes, that is my understanding at the moment. Just a note, plants also have a metabolism and release organics in water.

    To be clear, there is no such thing as organic nitrate and inorganic nitrate, see above post. Nitrate is just NO3-. I take what you've written to mean nitrate derived from organic sources vs nitrate added in this form to the aquarium. Stepping off the soap box.

    If nitrate is already plenty in the water column (30mg/L for example), then adding more will only produce small benefits for plants. The small benefit comes because with higher concentrations it becomes easier for plants to uptake the NO3 (up to a point of course). And this is under the hypothesis that the other nutrients are non-limiting, light is plenty and plant metabolism has more to give. And here is a hidden benefit of dosing a complete fertilizer... While true that dosing nutrients to the aquarium will not remove organic molecules, plants can create a good environment to accelerate their degradation mainly by providing O2 to the substrate and water. Remove the limiting factor in plant growth and overall tank health will improve.

    As you said above, in heavy stocked tanks it is good practice to remove waste as much as possible and do frequent, large, water changes. This is done by most fish breeders and fancy fish keepers I know, irregardless if they keep planted aquariums or not. Most do not have many plants in their grow-out tanks because they cannot remove waste that well. Such practices are done to remove organics before they get the chance to get to nitrate and release other nasty side products (see Tom's post). So I think you answered your question... If you keep up on maintenance in heavy stocked tanks you will not have enough nitrate for plants. I know in some of my tanks with heavy light, CO2 and many stem and floating plants, if I dose everything else but N I will run out in under a week. Unlike NO3 coming all the way from fish waste, dosing NO3 from inorganic molecules does not add a lot of side products/signaling molecules/inhibitory molecules etc.

    Don't get stuck on only thinking about NO3 because you can measure it, think about the other molecules that cannot be measured. Fish folks got stuck on pH for decades, whereas practice shows pH on its own is not a determining factor..TDS, GH, KH may be much more important.
     
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