Is Redfield ratio of 16:1 for N:P or NO3:PO4?

https://www.triton.de/en/

Tim Olson

Love to Learn!
View Badges
Joined
Feb 25, 2017
Messages
380
Reaction score
236
Location
Grosse Pointe, Michigan
I have a question on what the Redfield ratio actual is.

I understand the N : P ratio is 16:1 of Nitrogen : Phosphorus, not Nitrates : Phosphates. Although, I see them being used interchangeably in R2R and other sites.

Below, I did my best at showing the differences and how to convert Nitrate to Nitrogen and Phosphates to Phosphorus. So in this example I used Nitrates of 0.5ppm and Phosphates of 0.021ppm. This yields an N : P ratio of 16.5 and a NO3 : PO4 ratio of 23.8, which are significantly different.

Therefore, it appears the ratio is actually 23.1 if we're measuring Nitrates and Phosphates.

Also, this thread is not intended to be a thread on what Nitrate and Phosphate levels should be, but rather more of a chemistry question.

Thanks for any help on this!

1614934116981.png
 
Aquarium Specialty - dry goods & marine livestock

ScottR

Surfing....
View Badges
Joined
Feb 12, 2019
Messages
7,987
Reaction score
26,529
Location
Hong Kong
All I know is that it’s impossible to chase these numbers in our closed systems. The redfield ratio also fluctuates in different parts of the oceans as well. What I’ve found is: find a number that works for the type of tank you keep and keep it there. But when we are testing our tanks, we are actually testing nitrates and sometimes nitrites. The purpose of this isn’t to chase the redfield ratio numbers.
 
OP
Tim Olson

Tim Olson

Love to Learn!
View Badges
Joined
Feb 25, 2017
Messages
380
Reaction score
236
Location
Grosse Pointe, Michigan
All I know is that it’s impossible to chase these numbers in our closed systems. The redfield ratio also fluctuates in different parts of the oceans as well. What I’ve found is: find a number that works for the type of tank you keep and keep it there. But when we are testing our tanks, we are actually testing nitrates and sometimes nitrites. The purpose of this isn’t to chase the redfield ratio numbers.
Thanks ... This question is more of basic question on how to calculate the Ratio, rather than whether we should chase numbers in a reef tank. Hopefully we'll get a solid answer on whether we should be using Nitrates/Phosphates or Nitrogen/Phosphorus to calculate the magic ratio.

Here's one example, from Redfield Ratio - an overview | ScienceDirect Topics, it states "The Redfield ratio is the ratio in which different chemical elements are present in average phytoplankton biomass. It defines the stoichiometry of photosynthesis and remineralization reactions. On average each atom of phosphorus in phytoplankton biomass is attended by 16 atoms of nitrogen and 106 atoms of carbon, and this C : N : P ratio of 106 : 16 : 1 is the most commonly used value of the Redfield ratio. This ratio is sometimes extended to other elements but is most usually restricted to C, N, P and O2."

I'm not an expert on this, so I hope I'm not misinterpreting the information.
 
Budmans

Hans-Werner

Well-Known Member
View Badges
Joined
Aug 24, 2016
Messages
796
Reaction score
959
Like your citation states the Redfield ratio is a molar ratio of N to P. This means each atom of P there are 16 atoms of N (as available N compounds).

Nitrate has a molar mass of 14 (N) + 3 x 16 (O) = 62
Phosphate has a molar mass of 31 (P) + 4 x 16 (O) = 95

If all nitrogen is oxidized to nitrate and nitrate would be the only available nitrogen compound the Redfield ratio in nitrate : phosphate would be 16 x 62 : 95 = 992 : 95 = ca. 10 : 1; maybe you already have read about this 10 : 1 ratio somewhere.

However this is of little value for corals, especially hard corals and here SPS and massive LPS, since in scleractinians living tissue is only a thin film over a calcareous skeleton of many times the dry mass of the living tissue. And this skeleton is not neutral to the nutrient consumption but nutrients are incorporated in a very different ratio than the Redfield ratio. Although this is little studied, in my experience corals consume nutrients in a much narrower ratio than the Redfield ratio.
 
OP
Tim Olson

Tim Olson

Love to Learn!
View Badges
Joined
Feb 25, 2017
Messages
380
Reaction score
236
Location
Grosse Pointe, Michigan
Thank you for your straightforward explanation. Now it makes sense to me.

With regard to the ca. 10: 1 ratio, I did run across this Redfield summary that stated 10.645: 1 for Nitrates: Phosphates, but I didn't really understand it. ... "The optimal C: N: P ratio found by Redfield is about 106: 16: 1 in molar terms, or about 41.1: 7.23: 1 when expressed by weight (e.g. in mg or mg / l) . Equivalent also to maintaining a weight ratio between Carbon, Nitrate (NO3-) and Phosphate (PO43-) of about 13.67: 10.645: 1"

I don't plan on using the Redfield ratio for my corals. Although, I wanted to understand how it's calculated, as an arm-chair chemist.

:)
 

Randy Holmes-Farley

Reef Chemist
View Badges
Joined
Sep 5, 2014
Messages
43,026
Reaction score
31,607
Location
Arlington, Massachusetts, United States
Although, I wanted to understand how it's calculated, as an arm-chair chemist.

That's great! :)

I'd note that the Redfield ratio is of almost no use to a reefer, and folks widely misunderstand what it really is and what (if anything) to do with it.

Even within the narrow selection of "macroalgae", it does not usefully describe their contents. In a single study of macroalgae growing at a single ocean site, the values for N : P ratio ranges over a factor of more than 5:

 

Hans-Werner

Well-Known Member
View Badges
Joined
Aug 24, 2016
Messages
796
Reaction score
959
In bubble algae (Valonia) the bubble is the vacuole filled with water, ions and sometimes organic compounds. The living tissue is the thin "peel" that is left if you burst the bubble.

More than 20 years ago I tested the "cell sap" from the vacuole of such a bubble alga for nitrate in a tank with nitrate below the detection limit and found very high concentrations of nitrate, 100 ppm or more. The nitrate has osmotic function. Unfortunately I did not test for phosphate but I doubt there was much phosphate in the vacuole.

This shows how variation in nutrient concentrations in organisms can arise. If by chance the nutrient ratios in a tank with refugium is complementary between corals and algae, adding nutrients in the Redfield ratio may work, by chance.
 
Lazys Coral House
https://www.triton.de/en/

How healthy are your fish?

  • All of them are Healthy

    Votes: 294 81.2%
  • Most of them are Healthy

    Votes: 44 12.2%
  • Half of them are Healthy

    Votes: 3 0.8%
  • Most are Unhealthy

    Votes: 4 1.1%
  • All are Unhealthy

    Votes: 5 1.4%
  • Other (please explain)

    Votes: 12 3.3%

Online statistics

Members online
2,373
Guests online
5,774
Total visitors
8,147
WWC
Top