Weekly nutrient consumption in planted aquarium

Discussion in 'Aquarium Fert Dosing' started by Marcel G, 1 Nov 2014.

  1. Marcel G

    Marcel G Guest

    I would like to share with you the results of my three-months experiment with real consumption of nutrients in planted aquarium.

    I weighed the plant biomass (live weight) which were produced in my aquarium regularly (after each trimming). Every time I did some trimming in my tank, I thoroughly shook the water down from plants and weighed it on a digital scale with an accuracy of 0.01 g. This way I monitored the biomass gains for 3 months, and finally I calculated the average weekly biomass gain: 12 grams of live weight for the area of about 35x35cm (60L). So each week approximately 12 g of plants grew up on an area of 35x35cm. Since this is a "live weight", in terms of dry matter that makes about 10% = 1.2 g of dry weight. And since we know that there is about 45% carbon (C), 2% nitrogen (N), 1% potassium (K), 0.2% phosphorus (P), and 0.02% iron (Fe) in plants' dry matter, it's relatively easy to calculate the actual amount of nutrients that plants needed for 12 grams of biomass per week: 2 g CO2, 1.8 mg/L NO3, 0.1 mg/L PO4, 0.2 mg/L K, and 0.004 mg/L Fe.

    I will add that in my aquarium, I use quite strong light (100-120 µmol PAR at the bottom), nutrient-rich substrate ADA Aqua Soil, I supply about 4.7 g of CO2 per day, fertilize as needed, and each week I change 50% of water. Details of the aquarium can be seen in my presentation (Nano 4).

    I will definitely continue doing similar tests (and perhaps some other users will join me to have more data from different tanks), but even so, I'd say that I came to quite interesting findings => that even a relatively densely planted aquarium with strong lighting and plenty of nutrients does not need weekly more than 2 mg/L NO3, 0.1 mg/L PO4, 0.2 mg/L K, 0.005 mg/L Fe. Moreover, from the weekly dose of CO2 that I'm adding into my tank (4.7g x 7days = 33 g), the plants actually consume only 1/16.

    Compare this with the amount of nutrients you supply weekly in the aquarium using different commercial fertilizers, if you stick to the recommended dosage:
    ADA = 1 mg/L NO3, 0.5 mg/L PO4, 25 mg/L K, 0.05 mg/L Fe
    Easy-Life = 2 mg/L NO3, 0.1 mg/L PO4, 5 mg/L K, 0.2 to 0.5 mg/L Fe
    Tropica = 6 mg/L NO3, 0.3 mg/L PO4, 1 mg/L K, 0.07 mg/L Fe
    PMDD = 1-5 mg/L NO3, from 0.1 to 0.3 mg/L PO4, 3 mg/L K, 0.1 mg/L Fe
    EI = 30 mg/L NO3 (= 15-times more), 3 mg/L PO4 (30-times more), 10 to 20 mg/L K (50-100-times more), 0.5 mg/L Fe (100-times more)

    PS: The above test doesn't take into account the increase in root biomass (only partially), which means that the actual nutrient consumption will be slightly higher. Some nutrients in the aquarium will be produced naturally in mineralization (conversion of organic matter into minerals) or may be present in the substrate, which means that the plants may get by with a smaller amount of added nutrients. On the other hand, the efficiency of nutrient distribution will certainly play some role also, as this efficiency will never be 100%, so for this reason it can be wise to use little more nutrients.

    Also, it's quite a known fact that the amount of phosphates have a huge influence on plant growth. When I limited phosphates in my fertilizing regime, my plants grew very slowly (perhaps only 5 g body weight per week) even under very strong light. But once I increased the concentration of phosphates to 2-3 mg/L PO4, the weekly gains increased to 25-30 g of live weight.

    My point is not to save some small amout of fertilizer, but rather to understand what amount of nutrients our plants really need, which in turn will help us to understand the usefulness or uselessness of some methods of fertilization. A lot of people grop in what fertilizing method (ie. which fertilizer) to use. As I stated above, different fertilizers have different composition of nutrients. If we know how many nutrients plants can consume under certain conditions (strong vs. weak light, lot vs. little PO4, lot vs. little CO2, etc.), we will know quite precisely what is appropriate dosage. As I demostrated on the example of my aquarium (strong lighting, lots of CO2), my plants will get by even with an extra-poor fertilizer like ADA, which still contains enough of everything, except nitrates, because the ADA relies on the fact that nitrogen compounds are already present in great numbers in ADA substrate (+ something is being produced in aquarium from fish). Virtually all fertilizers (except EI) use relatively moderate concentrations of nutrients ... but these levels are still several times higher than our tank will in most cases need. So although I would use Tropica fertilizer in my aquarium, still the plants there will have a galore of nutrients (= practically non-limiting amounts). EI method in this regard is completely "overstated" because it uses 15-times higher amounts of nitrates, 30-times more phosphates, ~100-times more potassium, and 100-times more iron ... than my plants need. As I said, with large quantities of phosphates the plants will grow faster, but is it desirable? I know no one (except the people who make a living selling plants), who would want each week throw away a bucket of plants. So my conclusion: Methods like EI and PPS-Pro are designed more for the avid plant growers; in normal plant aquarium I would probably not recommend them to anyone (although I was formerly rather their advocate). And the argument that excess nutrients has no effect on algae, I do not consider valid. It's certainly reasonable to use a little more of fertilizer than is the "real" consumption, because the effectiveness of its distribution is certainly not 100% (due to imperfect flow; part of the micronutrients deteriorate before it gets to the plants, different plants have different demands, etc.), but how much more ... 2- to 3-times more? Definitely it's not necessary to use 100-times more.

    I know that many EI advocates will argue that larger amounts of nutrients don't pose any risk (although I don't think so). Still, it can be useful to know what's the real nutrient consumption in our tanks.
     
    Last edited by a moderator: 1 Nov 2014
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  2. Martin in China

    Martin in China Forum Moderator Staff Member

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    Even if EI is 100x more than needed, it is still 200x cheaper.....
    Anyway, what you are saying is that we could use EI, but a lot less of it?
     
  3. pepedopolous

    pepedopolous Member

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    I think it's well known that EI is all about over-supply. Got me thinking though... if plants need such small amounts, why should we dose EI macro and micro ferts more than once per week?

    P
     
  4. Tim Harrison

    Tim Harrison Global Moderator Staff Member

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  5. Marcel G

    Marcel G Guest

    EI was never meant to be applied rigidly ... but did you know that most people (who are using this method) are dosing probably 50- or 100-times more nutrients then needed? Do you know that all these people believed Tom Barr's estimate ... but it seems that this estimate is extremely overestimated?! Tom Barr never mentioned elsewhere how he figured out, that this amount of nutrients is the "sweet unlimiting spot". I just marvel at why no one ever questioned these amounts. If it's true that most planted tanks have such a low nutrient consumption, then why to dose 100-times higher amount if 5-times higher amount would be "unlimiting" in the same way? Why? Because it's still safe for critters? Or because I have not a better idea (better estimate)?

    When I dose 4 mg/L NO3, 0.2 mg/L PO4, 0.5 mg/L K and 0.01 mg/L Fe weekly in my heavily planted tank with extra strong light, high stable level of CO2 and ADA substrate, then I'm already using "EI" method.

    I don't care what other people are adding to their tanks. If someone wants to add 100 mg/L NO3 or 30 mg/L PO4, its his choice. My goal in doing this test was to find out what my plants really need. Based on this I can supply them with enough nutrients without going to extremes and creating "nutrient solution culture" for algae.
     
  6. Martin in China

    Martin in China Forum Moderator Staff Member

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    I am using EI as much as you mentioned...here is the thing, I had some problems before with GSA so I dosed more PO4 and indeed it helped, I also had some BGA so I dosed more NO3 and this also helped. If we dose too much than how is this possible?
    I'm not trying to attack you in any way, I just want to understand.
     
  7. Marcel G

    Marcel G Guest

    There is a difference between what plants may need, and what can inhibit algae in one way or another. So while plants get by with such a small amounts of nutrients, in case you have GSA problems, then it's maybe wise to add more PO4 (and the same logic applies to BGA and NO3). I did not want to say that people should decrease their dosages (as I said, it's entirely their fight - their choice). Do whatever you want. My point was just to show the results of my test, to show that our plants probably don't need 100-times more nutrients like EI suggests. So if you dose more PO4 ... you do it for eliminating the problems with algae, not to supply your plants with enough nutrients. So if someone suggests using higher levels of nutrients (like PO4 or NO3), it's not because the plants really need it, but because algae hate it.
     
  8. Martin in China

    Martin in China Forum Moderator Staff Member

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    Good point
     
  9. pepedopolous

    pepedopolous Member

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    If I recall correctly, Tom added progressively more and more nutrients to an aquarium with an insane amount of lighting and CO2,
    to the point where adding any more nutrients did not result in any increase in growth.


    P
     
  10. Crossocheilus

    Crossocheilus Member

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    What I am about to say is NOT based on any science or experimentation or experience, just a thought....

    Perhaps the plants only actually use a small amount of the mineral ions we provide, however it is the availability of them in the water that means that they never have a lack of it.
    E.g.
    If all they need was 2ppm of nitrate and all that was in the water was 2ppm of nitrate then the nitrate that they needed, although enough was present, would be scarce and thus not always available exactly when and where it was required? By having an excess in the water column at any given leaf their is an abundance of, in this case, nitrate. This means that nutrient uptake is very efficient and the plant or part of a plant is never left without any (nitrate)

    Although come to think of it good flow should prevent that problem (?)

    Sorry if that makes no sense or is of no help...
     
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  11. Michael W

    Michael W Member

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    In this article http://www.barrreport.com/showthrea...I-can-get-you-there-with-a-small-modification Tom Barr commented on dosing only what is needed for plants to grow but observing the change in the plants growth. He suggests that you can dose the standard EI and lower the amount until you reach a point where you see the plant show signs of struggle, you then gradually dose more to find an optimum level which will encourage growth without over dosing every time.

    Good flow helps a lot of problem and you mention a really good point. If someone can't achieve a nice flow, plants may not do well in receiving the nutrients, a way around it would be to dose more and hope for the chance of contact between nutrients to increase to compensate for flow.

    I use the duckweed index proposed by Darrel to dose my low tech tanks, which is similar to the method I linked posted by Tom Barr except you monitor the growth of floating plants and dose if the floating plants don't look so good. This is effective because floating plants receive more light than those fully submerged, they have access to unlimited CO2 therefore, the limiting factor to their success is nutrients.
     
    Last edited: 1 Nov 2014
  12. Tim Harrison

    Tim Harrison Global Moderator Staff Member

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    I think that Tom also mentions that EI can be fine tuned...the dose can be steadily reduced until the signs of deficiency occur and then notched back up to the previous dose.

    Edit: Thanks Michael that's the link I was looking for when you posted, and beat me to it.
     
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  13. Marcel G

    Marcel G Guest

    I cannot imagine how he could do that ... how he could find this out. How was he doing such a test? Tom Barr is very taciturn as far as explaining his methods/methodologies. BTW, is anyone of you using "insane amount of lighting and CO2"? So even if I admit that his nutrient estimate (EI) could be valid for some extreme situation, my situation was definitely different ... although I was using 120 µmol PAR in my test, and high levels of CO2 (also in my tank, the dissolved organics are virtually undetectable according to the lab analysis, the dissolved oxygen level is around 10 mg/L during photoperiod, the flow is good, most of my plants are pearling). What light should I use so that my plants will need 15-times more NO3, 30-times more PO4, and 100-times more K and Fe? 700 µmol PAR at the substrate? Is 700-1000 µmol PAR at the substrate a normal environment in our tanks? Absolutely NOT !!! So why should I follow that estimate (EI) if the conditions on which it is based are absolutely unrealistic?
     
  14. Crossocheilus

    Crossocheilus Member

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    Location:
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    Because no matter how many plants you have or how ever high your lighting is you will NEVER run put of nutrients meaning plants never get deficiencies or stunted growth, as a whole plant or as one cell.
     
  15. Marcel G

    Marcel G Guest

    So if I understand that correctly, I should put into my tank whatever Tom Barr says, because he says that my plants will never be limited at these amounts. Well, then I have another estimate for you: Eat 50-times a day, and eat really big portions like professional bodybuilders ... because if you eat that amount of food, you'll NEVER be hungry !!! This is exactly the same logic. No matter that you're not any professional bodybuilder, no matter that you NEVER burn such a high amount of calories ... just do it !
     
  16. Michael W

    Michael W Member

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    889
    I don't follow the EI guidelines but to me EI lets you get away with over dosing. It allows flexibility and really It doesn't make a lot of hassle, just drop some salt in and that is that. As far as I can see Tom Barr doesn't dwell on specific measurements, he proposes his dosage but I don't see him just advocating them, he has written different methods of dosing to suit the needs of the hobbyist as seen in the link I had provided.
     
  17. Tim Harrison

    Tim Harrison Global Moderator Staff Member

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    Not sure that's a particularly good analogy...but I guess it is easy to misunderstand the principles of EI, I know I did at first, but if you read the links posted above I'm sure you'll gain a better understanding.
     
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  18. Marcel G

    Marcel G Guest

    If you read my first post I hope you'll gain a better understanding of my point. ;)
     
  19. Marcel G

    Marcel G Guest

    I'll comment some sentences from the barrreport.com (see post #11 by Michael W):

    1) First of all, Tom B. says that for most aquariums the critical point is somewhere about 1/4 EI, and that very high light tank might consume as much nutrients as EI supplies. Do you think my tank uses a "very high light"? Do you think that 120 µmol PAR at the substrate (and about 400 µmol PAR at the surface) is high enough? I would think so. But maybe I'm wrong. So how it is possible that even under such a high light my plants consume only 1/15 of NO3, 1/30 of PO4 and 1/100 of K and Fe?

    2) What a humble statement! Tom B. thinks that EI is the only method ensuring an unlimited amount of nutrients. If my plants need only 2 mg/L NO3, 0.1 mg/L PO4, 0.2 mg/L K, and 0.004 mg/L Fe weekly ... and most commercial fertilizers supply more than that ... does it still mean that the only method ensuring unlimited amounts of nutrient is EI? Hardly!

    Do you really think that adding less then 15-times more NO3, 30-times more PO4, 100-times more K and Fe is bad for hobbyists? Do you think that 5-times more NO3, PO4, K, and Fe is not sufficient for good growth?
     
  20. parotet

    parotet Member

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    Subscribed... This discussion is extremely interesting. Thanks Marcel for sharing your results. Looks like a lot of work has been done. Will you include an extended version of this experiment in your website? This is a promising thread!

    Jordi
     

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