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Ideal fertilizer ratios for dosing, are my calcs correct?

Discussion in 'CO2 Enrichment' started by jeremy v, Sep 17, 2008.

  1. jeremy v

    jeremy v Guru Class Expert

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    Quick question,

    Tom has mentioned in different posts that aquatic plants are usually around 7-1-8 N-P-K by mass. That would mean that dosing those nutrients in that ratio would be ideal, wouldn't it? Not necessarily for plant growth, but just so that you aren’t needlessly wasting any nutrients. My question is this. The N-P-K ratio is a ratio of Nitrogen-Phosphorus-Potassium like it is for land plants, not NO3-PO4-K (Nitrate-Phosphate-Potassium), like we calculate and dose for right? So to get a true ratio for ppms of Nitrate-Phosphate-Potassium you have to factor in the Oxygen components and their masses to get a true ideal ppm ratio?

    I am asking because Tom has mentioned that you actually get plenty of potassium just by dosing KNO3 for nitrate, and that would only be true if the N-P-K ratio was actually for Nitrogen-Phosphorus-Potassium. I just want to make sure I am not under dosing Potassium and/or confirm that if I dose KNO3 for nitrate that I don’t need to bother with any additional potassium fertilizer.

    With my quick calcs, I came up with a converted ratio of about 31-3-8 for a mg/L or ppm comparison of NO3-PO4-K for ideal dosing. That ratio would explain why Tom has said that dosing potassium in addition to what is obtained from KNO3 is unnecessary.

    I realize that what matters most is making sure there is at least some of each nutrient and the ratio isn’t really critical, but I am mainly doing this as my way of trying to create the most nutrient balanced “leftover water change water” for use on my houseplants and yard plants. Also it can save me some money on ferts when I eventually start adding a few more planted tanks to the mix too, haha.

    I am also trying to get my dosing as consistent as possible so that I can pretty much test only nitrate levels (if I ever need to), and easily know that if I have enough that all the other nutrients are all fine to help with troubleshooting.

    Any confirmation/correction would be much appreciated.

    Have a good one, Jeremy
     
  2. tedr108

    tedr108 Lifetime Charter Member
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    Jeremy,

    If all plants used the same ratio and amount of nutrients all of the time, you might be able to get this to work. However, Tom has mentioned that the usage of nutrients is variable by plant type and by constant changes in the tank. Plants grow and use more of some nutrients, but they also block light from other plants. Your fish grow or multiply or some die off and now your nitrates/phosphates vary because of that. I think to do what you want to do would require some serious and expensive testing kits, and you would have to test often. I think that's why EI came into being ... add extra inexpensive nutrients (incl. CO2) and a good amount of light so there are no limiting factors on plant growth and let them go to town. Then, avoid overdosing too much by doing water changes.

    I'm no expert, but that's my take...
     
  3. Carissa

    Carissa Guru Class Expert

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    I would be interested in understanding this ratio as well. According to calculations on this site:

    Calculating dosages of fertilizer elements for a planted tank

    Adding 1 tsp of KNO3 to 50 gallons of water results in:

    11.45ppm potassium
    18.14ppm nitrate

    So you're getting about 1.6x the amount of nitrate as potassium. This obviously does not coincide with the ratio of 7N:8K. It also doesn't seem to fall in line with the suggested ppm's of nitrate and potassium being roughly similar, 10-30ppm, unless the idea is that you end up overdosing nitrate to keep potassium high enough. Which could be the case. If this is the idea, adding K2SO4 would just eliminate the need for as much KNO3.

    At this point I don't understand why factoring in the oxygen components would make sense. KNO3 means 1 K, 1 N, and 3 O.
     
  4. VaughnH

    VaughnH Lifetime Charter Member
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    Tom developed the EI method for those of us who don't particularly enjoy nor ever master the art of getting just the right amount of each nutrient in the tank at all times. He discovered that you can have several times the optimum concentration of any of the fertilizer components in the water, and the plants and fish show no ill effects from it. This is liberating! Add to that the realization that if you get rid of half of the water in the tank once a week, the maximum concentration that can ever build up in the water is twice the amount you dose in one week, which is well within the limits on any of the fertilizers based on doing harm to fish or plants. Now, you are really liberated, and you can be very relaxed about the actual, exact needs the plants have for nitrogen, phosphorous, potassium and the various trace elements. That lets us enjoy doing aquatic gardening without what to some of us is the drudgery of testing water, carefully weighing fertilizers, following an exact routine when dosing, etc.

    Tom also tested the various ratios that were touted as being required by plants, and found nothing to recommend paying any attention to them.

    And, with all of that testing, Tom also found that nothing involving the type of overdosing EI recommends causes any algae to start growing.

    I know we are all already aware of all of that, but when we start discussing ratios, exact fertilizer amounts, etc. I like to go back and think about how we got where we are today.
     
  5. jeremy v

    jeremy v Guru Class Expert

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    Vaughn,

    I totally agree with all of that and I love that aspect of EI. That's why I use it myself right now and I dose so that all nutrients are in excess at all times. Others might get excited by being able to grow plants well just by using EI, but for me my greatest interest in this hobby is not only creating a beautiful tank, but to have the challenge of also growing the most healthy plants possible with the least waste of any input to the system (due to unnecessary imbalances), least light possible, and most efficient use of all elements related to the tank. I come mainly from a mechanical and electrical engineering background and I have always loved trying to design things that achieve everything desired in as simple of a way as possible. That to me is good engineering and design. That's why I am bringing this stuff up and asking about it. I agree with you as well, if anyone reading this is just wanting to grow plants well and that's it, they might not want to read the rest of this post, haha.

    Everyone,

    Ppm is a concentration, but it just so happens that in water it converts to mg/L perfectly (1:1). 15ppm (in water) is the same as saying there is 15mg of Nitrate (NO3) per liter of tank water.

    Nitrate is NO3, and each of those atoms that make up nitrate have mass to them. N weighs 14.0g/mol and O weighs 16.0g/mol, so one mol of nitrate weighs 14.0g + (3 x 16.0g) = 62.0g. That means that for every 62 grams of nitrate you put in the tank, 14g of that is actually nitrogen.

    Nitrogen is the component referred to in the ideal ratio of N-P-K from Tom of 7-1-8, not nitrate. That's what I meant by the "oxygen" needing to be factored in for proper conversion to a useful ppm ratio (for us in the aquarium field). The same issue exists between P and PO4 (phosphorus and phosphate) and needs to be accounted for. When you do that you end up with a ppm ratio of 31-3-8, so that means that ideal use of our dosed nutrients would occur (if fish waste is only contributing minimally to the system) if you dosed a tank in a ratio of 31ppm nitrate to 3 ppm phosphate to 8 ppm potassium. You get more than double that ideal potassium ratio just from dosing KNO3 for nitrate, so in reality, just dosing nitrate with KNO3 is already at least double dosing potassium without any additional potassium being added at all!

    I risk being cast out of the planted tank arena (haha) by bringing the dreaded "Redfield Ratio" (dun dun duuun) into this as well. Tom and others have talked about it before, but I will mention it here anyways. I see the problem with the Redfield Ratio not being in the ratio itself, but in the conversion used with it when trying to apply it to aquarium dosing. The Redfield Ratio is an atomic ratio, not a mass or ppm comparison. Once everything is all converted to the same units it ends up about exactly the same. The Redfield Ratio says that almost all plant and animal life in the world's oceans have a consistent internal ratio of carbon to nitrogen to phosphorus (C-N-P) of 106-16-1 by number of atoms. If you convert that to a mass ratio in order to make a direct comparison with fertilizer ratings, you end up with a ratio of 7.2-1 N-P instead of 16-1 N-P. That is almost exactly the same as Tom's 7-1-8 (7-1 N-P).

    You probably noticed that I mentioned that the Redfield Ratio was for ocean plants and animals, and not freshwater plants. I think it is interesting how the ratio ends up being exactly the same as what it is in freshwater plants. If the majority of the world's fresh and saltwater plants and animals are all optimized for this ratio of nutrients internally, then why wouldn't it make for the most efficient plant growth to dose in that same ratio?

    To me it is exciting to find similarities like that between the living things on earth. That sort of stuff is not necessary for healthy plants, but it adds to the enjoyment of having a planted tank (for me anyways), because my learning related to the aquarium now begins to apply to all sorts of other areas of my life and a greater total wisdom can be gained from the same level of study.

    Have a good one, Jeremy

    P.S.- I hate it when my mind suddenly fills with questions and ideas right before Tom announces that he will be gone for a while. It is hard to find the answers to this stuff and make sense of it all by searching online. That's why I want to take this time to thank Tom for having this site and putting the effort into it that he does, because without this site we would all be worse off in one way or another. It is very valuable having a resource that actually tests this stuff and can answer questions like ours without it all just being repeated theories that may or may not have any validity.
     
  6. jeremy v

    jeremy v Guru Class Expert

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    Tedr108,

    Do you happen to have any links to Tom's comments regarding this, because I would like to investigate that further. I tried doing a few searches of this forum and couldn't seem to connect with anything that fit. If that is true there is something I am missing here and I want to see if I can figure out what it is.

    Have a good one, Jeremy
     
  7. tedr108

    tedr108 Lifetime Charter Member
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    Jeremy,

    I will look for them and get back to you later. I'm almost certain that he did say that, but I may end up with egg on my face on that one. :) Maybe someone else here remembers and can pipe in...

    I do remember from my terrestrial gardening days fertilizing different plants with different ratios. I always assumed that was because the plants used nutrients at different rates. I don't see why aquatic plants would be any different.
     
  8. jeremy v

    jeremy v Guru Class Expert

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    Last night I came across an archived post by Tom (from 2005) that actually talks about the ideal ratio of 7-1-8, and it actually lined right up with what I was asking and confirmed my thoughts, so I thought I would post the quote and link here so others can read it. He explains it all better than I was as well, so it might make more sense to anyone that was confused by my posts and explanations.

    Re: [APD] Macro nutrient ratio

    Now I just have to look deeper into whether or not plants absorb nutrients in different ratios at all and if they do, why. What Tedr108 mentioned about surface plants needing different levels of nutrients, and how that's why there are so many different fertilizer formulations out there was an interesting a valid point to consider.

    I always just assumed that the different formulations were there to help you to balance out whatever your base soil had (or didn't have) to end up with good ratios, or else it was a purpose based fertilizer designed to boost one nutrient just to temporarily increase blooming, growth, color, etc. I am going to have to look into this more.

    Have a good one, Jeremy
     
  9. Carissa

    Carissa Guru Class Expert

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    Got it. So why is it that it's recommended that you maintain 5 - 30ppm of nitrate, and 10 - 30ppm of potassium? That recommendation doesn't make sense anymore.
     
  10. ceg4048

    ceg4048 Lifetime Charter Member
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    The suggested nutrient concentration levels are given by EI to ensure that the levels of nutrients are unlimited without regard to ratios. Chasing ratios based on atomic or mass ratios is futile because the uptake rates of each individual species as well as each individual plant within the species varies depending on light intensity, weight, temperature, available CO2, diurnal rhythms as well as the concentrations of available nutrients themselves. Even if you had a tank full of a single species and if you did dose per some "ideal" ratio the bio-mechanical inefficiencies in the system will prevent uptake at these ratios. The mechanism of nutrient uptake depends on osmotic forces as well as anion attraction and transport methods. Inefficiencies due to flow rates, friction as well as losses due to other organisms in the tank that can uptake inorganic forms of nutrients as well as to produce organic forms of nutrients means that the ratios will never be realized within the tank.

    Plants are not a simple linear system like a spring where you can apply some coefficient or constant and predict the outcome. There are so many different forces acting on them, varying from the quantum physics of light absorption, to the electrochemistry of compound production to the pneumatic and hydraulic forces within tissues. There is no grand unified theory for plants that will allow one to predict exactly what their uptake will be at any given time. This would be like predicting how you will feel next Monday.

    What EI is able to predict, based on empirical data is that under near ideal and unlimited conditions, under maximum lighting there is a maximum composite uptake of so many ppm of each nutrient. You can take these individual ppm values and perform whatever gymnastics desired but this will not mean that on any given day a given plant will uptake anions and cations in some specific ratio.

    The ratios only become relevant when there is a shortage of one or more nutrients.

    Cheers,
     
  11. tedr108

    tedr108 Lifetime Charter Member
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    ceg,

    I've come to the conclusion that you are some sort of plant biologist. :)
     
  12. Carissa

    Carissa Guru Class Expert

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    To me, the whole idea of EI is using ratios in a rough sense. If not, why not just dump in a cup of each fertilizer? Why measure 1/4 tsp of this and 1/16 tsp of that if ratios are completely thrown out the window? EI is using ratios, just in a very rough estimate and not to be exacting, but to overdose on those basic ratios to ensure nothing becomes limited. So the ratios must be predictable, true, within a margin of error. That's what the whole premise of EI is based on.
     
  13. VaughnH

    VaughnH Lifetime Charter Member
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    EI is based on the concentrations of each fertilizer that will ensure that none of them will ever be too low, plus the weekly water change to ensure that none of them will ever be too high. It isn't ratios, it is just that the plants need differing amounts of each of the fertilizers - a lot of nitrates, a lot of potassium, but not so well defined, a little phosphate and a little trace mix. Remember, the dosage amount for a 20 gallon tank is the same as for a 10 gallon tank, so no exactitude is involved.
     
  14. ceg4048

    ceg4048 Lifetime Charter Member
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    No mate, far from it. I just study what the real plant biologist has to say.:cool:

    If you follow this ratio path you're bound to paint yourself into a corner. We can calculate ratios for anything we can measure. How about the ratio of Carbon to Nickel in your daily diet? Can that ratio be calculated? Sure, but is it relevant? Not really.

    Don't approach EI within the context of ratios. Of course you can dump a cupful of everything in the tank and this too would be OK but why bother when the empirical data shows that the plant consumes 50,000 more Carbon than Nickel? Does that make economic sense? I don't think so. What happens if I dose a C:Ni ratio of only 30,000:1 is that a problem? It will depend on whether there is sufficient C being injected. On the other hand I can dose per molar ratio, say 50,000:1 and still be in trouble if my CO2 injection rate is poor.

    Some elements within cellular metabolism are expendable or are consumed in a way that makes some of their compound formations irreversible while other elements can be recycled easily. Carbon is fundamental for structure and food production so the plant needs mountains of it. Nitrogen is needed for chlorophyl production and is an integral component of DNA/RNA so a lot of this is also needed. Phosphate on the other hand is highly recyclable since it is a principal component of recyclable and dynamic compounds such as Rubisco, RUBP, NADP as well as ADP and ATP.

    So not as much P is needed as N or C but if the plant is short of P this compromises it's ability to manufacture or allocate these vital compounds. The severity of the shortfall now depends on the ratio of P to the other elements.

    Certainly, within the cells there are ionic balances/ratios which do matter. A typical example is in terrestrial plants or in emmersed mode where the ratio of K+ to Ca+ has an effect on osmotic forces and determines the "plumpness" of the cell. This is useful in the stomatal guard cells and determines the opening and closing of each stoma. This then regulates gas exchange (CO2/O2). As long as there is enough K and Ca available we wouldn't have to worry about this ratio because the plant figures that out for itself. Again, if the plant falls short of one or the other then yes, this ratio all of a sudden become important. But trying to micromanage this via dosing a specific ratio is absolutely pointless. We could never get it right.

    Ratios are therefore just a statistical exercise and are meaningless under non-limiting conditions. It's better instead to consider threshold ppm values below which we should avoid. Dose the max and let the plant figure out about ratios.

    Cheers,
     
  15. jeremy v

    jeremy v Guru Class Expert

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    Carissa,

    I think we are both on the same page in our thinking and that's kind of why I wanted to ask this stuff to begin with. I want to personally understand all of this better, and at the same time I don't think I am the only one that sees a discrepancy that at least needs to be asked about or ironed out for better congruity.

    Ceg,

    In my mind we are both saying the same thing completely, but that doesn't seem to fit (in my mind at least) with what we actually do in practice. That's why I need the help to figure out the discrepancy.

    Everyone,

    In my mind, if something is valid, it should all fit together with everything else around it like a puzzle, and there should be nothing out of order when it is questioned or put under scrutiny. I think that EI is legitimate enough that it deserves the honor of being scrutinized by the experienced (and the newbies) in order that over time it might become even better. These are my remaining thoughts related to the 31-3-8 stuff, because this is what I am still seeing, and to me it seems off-

    EI target ranges from this forum for high-light CO2 injected tanks-

    CO2 range 25-35 ppm
    NO3 range 10-30 ppm
    K+ range 10-30 ppm
    PO4 range 1.0-2.0 ppm
    Fe 0.2-0.5ppm or higher
    GH range 1-2 degrees "extra" 17-40 ppm or higher

    I am only going to focus on NO3, K+, and PO4 for the rest of this post in order to simplify things. In my mind, potassium doesn’t need to be nearly that high to remain non-limiting in all circumstances (according to Tom’s explanation and quotes related to 31-3-8 ratio of NO3-PO4-K that I just posted in this thread), and PO4 actually needs to be higher in order to truly be non-limiting, based on that same ratio of nutrients within dry plant mass.

    If that ratio is an average of all macrophytes (of which I sort of remember Tom saying that he personally tested ~45 different plants as well), that means that some plants need more (and some need less), so shouldn’t we at least be making sure that we are dosing the average value (based on average plant dry mass of 31-3-8 ppm ratio of nutrients) at all times as an absolute minimum? It doesn't seem like we have that as of yet in current dosing. When I also factor in (within my own mind, haha) the info learned from “The Relative Nutrient Requirements of Plants”

    The Relative Nutrient Requirements of Plants

    which shows that growth is increased by providing nutrients to “luxury uptake” levels, I end up with the following. You might think I am trying to use less nutrients and scrounge for efficiency, but I am actually saying that I think the current accepted balance is confusing to me, because it seems sort of arbitrary and too lean in some ways and needlessly excessive on others (dosing much higher levels of potassium in comparison to what is needed for non-limiting status).

    I see the ideal minimum weekly dosing as being the amounts I have below. I see the listed ppms as being the absolute minimum weekly dosing to assure that nutrients are never limiting growth at all and that the nutrient levels also remain in an efficient “uptake range” for the entire week. Excel tanks fit somewhere in the middle of the two tables below. The tables are based on Tom saying that the most demanding tank needs 2-3ppm of nitrate a day, multiplying by 7 (for 7 days between water changes), and then adding a few more ppm's to ensure that the nitrate is always being absorbed efficiently and in a zone of near "luxury uptake". Then I am scaling all other nutrient amounts from that number for nitrate according to the 31-3-8 nitrate-phosphate-potassium ratio within the average plant's dry mass.

    Low light and/or non-CO2 minimum total weekly dosing levels-

    NO3- 10+ ppm
    K- 3+ ppm (much less then current dosing while still completely non-limiting)
    PO4- 1.0+ ppm

    High light and CO2 minimum total weekly dosing levels-

    NO3- 30+ ppm
    K- 8+ ppm (much less then current dosing while still completely non-limiting)
    PO4 - 3.0+ ppm (50% more then current dosing in order to actually be non-limiting, even for average plants)

    Anything more is perfectly fine, and actually helps by adding stability to the system as a whole, but is not necessary for good non-limited growth.

    To add to that, it doesn’t benefit anything by just increasing one nutrient from those levels. All that does is add a factor of safety to one specific nutrient, not to the system as a whole. The key though is that the system as a whole is what matters most, and you are only as strong as the weakest link. That would mean that it would be most beneficial (to the system as a whole) to adjust/increase all nutrients according to the same ratio (31-3-8) shown above in order to add factor multiples of additional safety to the entire system (if desired). Those safety margins would allow you to possibly accidentally miss a dose or get behind in your dosing (for one reason or another) and everything will still be (as close as we can possibly estimate) equally buffered according to whatever safety factor you added to your dosing.

    As an example, you can add a 33% (0.33) factor of safety to the above "High Light" dosing by increasing NO3 10ppm, K 3ppm, and PO4 1.0ppm. If you only increase one or two of these nutrient levels your safety factor never changes at all, because the other links in the nutrient chain haven’t changed, so they will still hold everything down and the nutrients that are at higher safety factors are of no benefit to you, because even when you accidentally miss a dosing or something they will be inaccessible to the plant because one of the other nutrients would have run out long before and stopped all plant growth.

    What I am wondering is why it is that the current accepted dosing for nitrate and phosphate are really close to the levels that are needed for non-limiting growth (and in one case it actually seems a bit too low) and yet potassium is recommended to be dosed several factors higher then what seems to be necessary at any level of growth?

    It just seems like a lot more potassium (and usually one more fertilizer powder) to dose for no reason. That’s all I was ever trying to ask about when starting this thread. That was the strange inconsistency in my mind. It is not strange because I don’t understand how EI works, but because it is a recommendation that does not even seem to be based on Tom’s actual words at all. That’s why I was wondering if there was something I was missing or if something has changed in our understanding of nutrients and dosing.

    If the potassium was already in the water from the tap I wouldn't even be asking this stuff, because it wouldn't take any effort to have it in the water, and it isn't hurting anything by being there, but why are we dosing so much potassium and aren't we just dosing it to levels that are of no actual benefit at all?

    If you are going to say that everything is taken in at different rates, and some things are reusable while others aren't that's fine, and I would have to imagine that does happen, but doesn't the overlying question still apply? The only place nutrients (that have no gas form) can go in a fish tank are into the plants or out with the water change, so if it is not going into the plants (and being reflected in their dry mass) isn't all that extra unnecessary potassium just ending up down the drain, and where is the extra needed phosphate coming from?

    I feel like things are starting to fit together within my head, and I thank you all for that, but I could wake up tomorrow and realize that I have it all wrong too. That's why I like getting all of your input and thoughts.

    You are all right, I could just dose everything according to plan without questioning it, and my plants will most likely always be fine, but I do like to understand what I am doing and why or else it doesn't mean anything to me. Anybody can take direction and not ask questions, but I don't think that's how true wisdom is found. That's why I at least have to ask and keep asking until I can make sense of it within myself. I hope you all understand.

    Have a good one, Jeremy
     
  16. tedr108

    tedr108 Lifetime Charter Member
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  17. jeremy v

    jeremy v Guru Class Expert

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    tedr108,

    Thank you for that link, that's exactly what I was looking for. I never found that thread when doing my searches.

    I have 0 nitrates from the tap, a low fish load, and if I don't dose nitrates consistently they always stay the same or go down. I dose all of my nitrate with KNO3, so I feel pretty confident now that I can actually delete the K2SO4 completely (at least to see how it goes). I mainly just wanted to make sure that my plant growth wouldn't to come to a screeching halt as a result of taking away the K2SO4 and now I can't see that happening at all.

    When you are trying to learn and fully understand new things it is often hard to tell the unique advice that is only specific to certain situations, from the general advice, and from the stuff that isn't true at all. Thank you for your help, and thank you to everyone else that contributed to this thread as well. Your right, the ratios that Tom mentioned are a little different from what I calculated and Tom has said elsewhere, but his conclusions were the same (and the extra conditions he added fit my tank perfectly), so that helped a lot.

    Have a good one, Jeremy
     
  18. Tom Barr

    Tom Barr Founder
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    I've never liked ratio theory for dosing aquariums.
    I've always suggested ranges. Not ratios between eachother etc.
    (Note: this was prior to anything to do with a single course in plant Science and long before I went back to college a decade ago).

    So schooling ain't got nuthing to do with this.

    In their book on Mineral nutrition of higher plants, Bloom and Epstein(Yes, that Epstein) both suggest ratios have little to do with growth rates. Bloom is my prof for the qualifying exam on the topic for mineral nutrition, both are UC Davis prof's.

    These guys are the top experts in the world on this stuff.
    I'm a mere humble little guy but I also know what I've seen and agree with their logic and with the results.

    I cannot rationally argue against it.
    I buy the argument.
    They have done good experimental test, they have very good results, it's not just their words alone, it's the facts.

    Non limiting nutrients have a wide "range".
    We find massive differences in the external environment vs the internal plant tissue concentrations(the part that really matters when dealing with limitations).........plants also play a very active role in uptake and have many methods for dealing with about anything the environment may throw at them.

    They are not nearly as sensitive as some aquarist and web folks like to imply. You can reduce the waste of costly fertilizers by doing tissue analysis(not ratios) at large scales, but for us?

    1 lb of KNO3 ain't much for us.

    Different issues, different economics and different goals.

    Regards,
    Tom Barr
     
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