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Some studies (see snippet below)> link the N : P ratio (and not their absolute concentration) to algae limitation and stimulation. For example, Barr's EI proposes a 10:1 N : P ratio. <

Other methods, such as the Redfield>suggest 16:1.

It's often useful to play a though experiment. If ratios of N : P :K are an important aspect leading to algae growth in aquariums then it will be easy to induce (and stop ?) algae blooms. The 'faulty ratios' will also be common across many tanks experiencing algae blooms and many concentrations (more on this later). We have seen such strong interdependence situations with the light-CO2-nutrients triangle.

If however the rations of N : P :Kare not an important aspect that determines algae growth in the aquarium there will be aquariums with algae and aquariums without algae at the same ratios, aquariums without algae blooms at a wide range of ratios. The experiments to induce the algae blooms would be non-repeatable or will not apply across a wide range of light, CO2 levels and concentrations. In practice other aspects will fix the algae bloom then coming to a "N : P :K ratio of algae limitation". In other words N : P :K would be just one of the many small factors that may or may not influence a little bit if there is a bloom or not in our aquariums.

TLDR: Makes sense, if N : P :K plays a very important aspect of algae blooms it will be very common across many other variables and it will be very easy to induce algae with it.

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?

The fact is that there are <

studies> <

analyzing> <

the role of> of the N : P, N : K ratio and other ratios and limitation factors in natural ecosystems. There are also studies suggesting the importance of <

the interplay between multiple factors>, which would be unsurprising since we are dealing with a dynamic <

complex system>. If there were definitive answers to these questions, then we wouldn't have so many different approaches to planted tank keeping but a general framework that would apply to a majority of setups, which is not the case.

If N : P ratios are relevant over concentrations then the same effect on algae amount and type will occur at

- 10 mg/L N ,1 mg/L P; N : P 10:1
- 0,01 mg/L N, 0,001 mg/L P ; N : P 10:1

-100 mg/L N, 10 mg/L P; N : P 10:1

If you don't get the same effect it may be more worth to look at concentrations than ratios.

The same rationale applies to effects of ratios on plant quality and growth rate. Few proponents of various golden ratios bother to test the same ratio across 2 logs of concentration to check if indeed it is the ratio that makes the effect. Quite the contrary, as more data comes in the same proponents of the golden ratio start saying ' it works across quite a large range of ratios', 'you don't have to be that specific' and add some footnotes ' as long as X is kept above this value'. The golden ratio remains as optimal somehow, just through inertia.

For example, Barr's EI proposes a 10:1 N : P ratio.

As far as I have seen the Estimative Index never recommended ratios, even less 10:1 N : P. In the

original article the recommended ranges for EI are:

"

CO2 range 25-35ppm

NO3 range 5-30ppm

K+ range 10-30ppm

PO4 range 1.0-3.0 ppm

Fe 0.2-0.5ppm or higher (?)

GH range 3 degrees ~ 50ppm or higher

"

If you really want to force ratios out them you have between 3.5:1 to 6.9:1 N : P--not 10:1. If you want to use the figures from

Rotala Butterfly | Planted Aquarium Nutrient Dosing Calculator for EI you still end up with a ratio of 4:1 N : P by mass, very far from the referenced 10:1. I have to think part of the high PO4 dosage is to counteract the phosphate fearmongering at the time EI was published, the nutrient fearmongering seems to be blooming again.