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Phosphate in tapwater

MichaelJ

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9 Feb 2021
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Minnesota, USA
It would be great if someone could explain in layman's terms what the crux of the matter is with fertilizer ratios pertaining to our planted aquariums? and what are the postulates either way? I don't know much about the biological reasoning behind NPK ratios for aquatic plant keeping. For a long time experts around here have been saying that plants don't really care about ratios... that is not to say that you can't lure out some marginal benefits from dosing at certain NPK ratios relative to concentrations, for instance to promote increased algae growth in a laboratory test or promote or suppress algae in radically different environments such as lakes or rivers, but it certainly doesn't seem critically important for a successful planted aquarium. For what it's worth, I've been dosing and 4 ppm of N and 3 ppm of P / 20 ppm of NO3 and 10 ppm of PO4 for a very long time in both my densely planted tanks and I have excellent plant health and zero algae to speak of.

Cheers,
Michael
 
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arcturus

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6 May 2021
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DE
It would be great if someone could explain in layman's terms what the crux of the matter is with fertilizer ratios pertaining to our planted aquariums? and what are the postulates either way? I don't know much about the biological reasoning behind NPK ratios for aquatic plant keeping. For a long time experts around here have been saying that plants don't really care about ratios... that is not to say that you can't lure out some marginal benefits from dosing at certain NPK ratios relative to concentrations, for instance to promote increased algae growth in a laboratory test or promote or suppress algae in radically different environments such as lakes or rivers, but it certainly doesn't seem critically important for a successful planted aquarium.
For what it's worth, I've been dosing and 4 ppm of N and 3 ppm of P / 20 ppm of NO3 and 10 ppm of PO4 for a very long time in both my densely planted tanks and I have excellent plant health and zero algae to speak of.
The main questions are as follows:
  • Does the ratio of nutrients at a given concentration suppress or promote algal blooms (and plant health)? In particular
    • What correlations are observable if nutrients are available at non-limiting concentrations?
    • What correlations are observable if the concentration of one or more nutrients is limiting?
    • Note: "nutrients" include all elements required for photosynthesis.
There are laboratory studies and analysis of natural systems that indicate possible correlations between nutrient ratios and concentrations and the promotion or suppression of algal blooms and plant growth. Nevertheless, in discussions related to planted aquariums such observations are often dismissed as being not applicable. Natural environments are certainly very different than planted tanks. This raises a second question: Is the response of a photosynthetic organism (especially algae) to nutrient concentrations and ratios in a planted aquarium similar to the response of the same organism in a natural or laboratory environment? If not, why?
 

MichaelJ

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9 Feb 2021
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Location
Minnesota, USA
The main questions are as follows:
  • Does the ratio of nutrients at a given concentration suppress or promote algal blooms (and plant health)? In particular
    • What correlations are observable if nutrients are available at non-limiting concentrations?
    • What correlations are observable if the concentration of one or more nutrients is limiting?
    • Note: "nutrients" include all elements required for photosynthesis.
There are laboratory studies and analysis of natural systems that indicate possible correlations between nutrient ratios and concentrations and the promotion or suppression of algal blooms and plant growth. Nevertheless, in discussions related to planted aquariums such observations are often dismissed as being not applicable. Natural environments are certainly very different than planted tanks. This raises a second question: Is the response of a photosynthetic organism (especially algae) to nutrient concentrations and ratios in a planted aquarium similar to the response of the same organism in a natural or laboratory environment? If not, why?
Thank you very much @arcturus for taking time to laying this out in clear terms. That is very helpful!

Cheers,
Michael
 

jaypeecee

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21 Jan 2015
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Bracknell
It would be great if someone could explain in layman's terms what the crux of the matter is with fertilizer ratios pertaining to our planted aquariums?
Hi @MichaelJ

I'm pleased that you raised this point. I would like to understand how it applies to the plants that we want* and those we don't want** in our tanks. And what I learned only yesterday is a new term for me. And that is - Colimitation and Optimal Nutrient Ratios. If you type the words in italics into a search engine, you should get plenty to read. But, it wouldn't make good bedtime reading. On the other hand, maybe it would. o_O

* e.g. Java Fern

** e.g. algae and cyanobacteria

JPC
 

MichaelJ

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Minnesota, USA
Thanks @jaypeecee,

Hi @MichaelJ

I'm pleased that you raised this point.
I am sure I am not the only one who was curious about the main questions here - always good to reiterate what is being discussed.

I would like to understand how it applies to the plants that we want* and those we don't want** in our tanks.
Yes, I agree... either way.

And what I learned only yesterday is a new term for me. And that is - Colimitation and Optimal Nutrient Ratios. If you type the words in italics into a search engine, you should get plenty to read. But, it wouldn't make good bedtime reading. On the other hand, maybe it would. o_O
I did a brief search on "Optimal Nutrient Ratios for aquatic plants" and must say not much came up - However, this one was kind of interesting. According to this, I should have the perfect environment in my tanks for BGA :eek:- and I haven't seen BGA for ages and only a bit of it while the tanks were maturing (always thought of BGA as a new tank problem). Of course, It is usually more complicated than one single factor... light intensity, other relevant water parameters and nutrient levels, plant mass, stocking level (i.e. organic waste build up) etc. likely plays a much bigger role than ratios when people are struggling with algae. But it's an interesting discussion nevertheless.

Cheers,
Michael
 
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jaypeecee

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Joined
21 Jan 2015
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2,702
Location
Bracknell
Hi @MichaelJ

A few of us here on UKAPS did an experiment some while ago because we too were interested in the Redfield Ratio. Please take a look at this:


But, following a lot of reading on this topic, I discovered that the Redfield Ratio was no longer considered to explain the stoichometry of freshwater algae, cyano and plants. At least, that's my recollection but I'll re-visit this soon.

JPC
 

ceg4048

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@ceg4048, I hear what you say about the ratios, but would it be normal for nitrates to be higher than PO4?
Hi,
Yes, in the EI scheme of things this is normal. One of the reasons is that much of the PO4 is re-used in various metabolic cycles, whereas generally, the N from NO3 is consumed to a much greater extent by the construction of components such as proteins and so forth. Phosphorous is actually relatively rare in nature and is highly sought after due to it's energy producing capabilities. On the other hand, Nitrogen is abundant in nature. Almost 80% of the air we breathe is composed of Nitrogen, for example. It shouldn't be surprising, therefore, that the relative amount of N versus other elements in organisms is high.
I am aware of reports of successful planted tank keepers that seem to show that these ratios are not relevant. But there are other successful planted tank keepers that report otherwise. Are any conclusive (scientific) studies that demonstrate that such ratios do not correlate to algal blooms in planted tanks? Can we dismiss N : P : K ratios, and other ratios such as Ca : Mg?
I'm afraid there is very little conclusive scientific studies demonstrating this. Any study we find is usually focused on natural systems. As you mention, all we have is empirical evidence, based on the results in our tanks. I've personally explored the ratios and have not found any correlation - as long as C, N and P are non-limiting. I've found the same applies to Ca:Mg.
Regardless i have suggested quite straightforward ways to support the hypothesis and form the start of a scientific basis with a series of tests where you can show how important N: P :K is. Others have tried here and there but they still end saying the things i quoted. Plants and algae are adaptable like that, few things break if you go from 4:1 to 3:1 especially when you are speaking about water concentration. Hypotheses abound, rather looking forward to the data. I have referenced the EI source as that is the source of the correct proposal/ratios for EI. Sorry if that offended you but thanks for making the core of your focus clear.
I'm not offended at all. What I try to make clear, especially to inexperienced hobbyists is that because of plants adaptability all we really need to do is to avoid the limitation of nutrients - and by this I mean specifically the EI suggested nutrients. There is another thread where someone attempts to delegitimize EI by substituting ammonium compounds in lieu of KNO3 and reports failure. Well, yes, unlimited ammonium can have negative consequences. I'll repeat what I recall mentioning in that thread, that some hobbyists assume they are reproducing the EI scheme and their failures are then blamed on EI or eutrophic dosing in general.
Hi @ceg4048

Please take a look at the following link - Tom Barr's entry. Then scroll down to Roger Miller's entry. I suspect the figures being discussed had their origin in the Redfield Ratio (RR). My understanding is that the RR is now not considered to be applicable to the aquarium ecosystem. At this point, it may be best to go to The Krib discussion:

Phosphorus
I'm sure you will have read this disscussion before but other UKAPS members may be new to it. OK, I now have a question for you. And that is - when you say "There is no relationship in our tanks of N to P ratios with algal blooms. The related blooms occur as a result of any limitation of N or P". Are you referring to all forms of N and P that exist in our tanks?
Hi jaypeecee,
Well, in a way this is kind of a trick question (kinda like when MonaLisa Vito is being cross examined by Prosecutor Jim Trotter in the movie My Cousin Vinny) . I was really only addressing the general EI NO3 vs PO4.
If we extend it to "all forms of N and P that exists in our tanks" then things become a bit foggy. There is, for example N and P bound up in organic waste, in living micro organism, in the sediment and so on and so on. No one can measure or account for all forms of N and P. We certainly can't measure these without specialized instruments, and even so, these values are constantly changing. We can only have precise control of what we dose.
Since I don't have control I'm saying that you can dose as much KH2PO4 as you want and as much KNO3 as you want without worrying about what ratios you dose. So for example you can dose the EI suggested KH2PO4 and then 5X the suggested KNO3 or vice versa. You can also dose any combination in between and not have any trouble as long as you follow the EI scheme regarding cleanliness, maintenance and so forth. Depending on your lighting, you can dose 1/2 EI or 3/4ths in whatever combination. As long as you do not go below the threshold for that lighting level or for the CO2 level then this will work. Members her have done this successfully, many times.

I think what happens is that we can become so hypnotized by some of these concepts and hypotheses that we lose the thread, so to speak.
EI also has the world view that neither nutrients nor nutrient ratios cause algal blooms, but that the blooms occur as a result of the conflict between algae and plants in a predator/prey relationship. Barr goes on to explain that malnourished plants are weakened and fall victim to the algae. Blooms can therefore occur as a result of many different scenarios within the tank that causes poor nutrient uptake by the plants in the tank. So blooms occur in a tank and the hobbyists immediately blames too much of this or that, or incorrect ratios, or a score of other possibilities.

Cheers,
 
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