# Redfield ratio and aquarist mistakes



## fritz (Jun 3, 2008)

Thanks for the *highly* informative post and the bookmarks


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## ikuzo (Jul 11, 2006)

plantbrain said:


> If you want to convert to NO3 and PO4 (note: this does not take into account any NH4 sources, thus this can skew your interpretation and increase the N ratio when you think it's actually much lower-especially true with high fish load/feeding, lower light etc) you need to add the molar weights of NO3 vs N and P vs PO4.


so what's the ideal ratio of NO3 : PO4?


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## Wasserpest (Jun 12, 2003)

ikuzo said:


> so what's the ideal ratio of NO3 : PO4?





plantbrain said:


> To convert to mass equivalents, you need to multiply the weight of N by 30.97 g/mole P divided by 14.01 g/mol of N= ~ 2.2
> So what was once 16:1, is now 7.2:1 N to P by *mass*.


Too early for math right now, but it looks like that pretty much sums it up!


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## plantbrain (Dec 15, 2003)

I do not think a ratio is really that applicable, okay so it might save a little wasted NO3 or PO4, not much in the larger scheme of things and KNO3, K2SO4, KH2PO4 are VERY VERY cheap, but more folks waste traces which cost much more.............and they dose those very liberally curiously enough:icon_roll 

It might help to predict how much to dose and if you want leaner ranges, but as long as you have non limiting ppm's of nutrients, and you do not get too far outside the ranges, say 100:1 N to P etc, I do not think it matters, the plant will take in the same amounts endogenously.

Exogenous concentrations really are not that critical if they are non limiting and do not approach excess levels.

Folks slip up, make assumptions, cannot test or answer a basic water quality question for the life of them, see one negative response and attribute it to "Excess Nutrients" without checking the rest of the possible causes they can think of well.

They ignore the observations that others do showing their conclusions are not correct. I know and understand folks want to be right and helpful in their advice, but wanting to and intent etc is not the same as being so. sometimes there's no really clear answer, so you go with the one that seems the best based on logic and try anb test to rule it out. You should have a humble and curious enough ego to learn and correct yourself as you discover new things.

If you happen on a method and it works for you, but you assume it works for the wrong reason, then you have some issues to work through. Still, many assume since it works, that's proof they are right.

It's not, not even close.
In this case, 2-3x off.
And for entirely the wrong reasons as to why. 

Yes, I keep about 5:1 ratio or so.
It use to be more in the 50-100:1 range when PMDD came about in the mid 1990's (Recommended ranges: 0.2ppm of PO4, 10-20ppm of NO3). I raised it to about 10:1 to 20:1, then 5:1 to 10:1 range which it is today. With more light, came more CO2 to match and more nutrients.

Over the years I've returned to the advice and issues and looked at them in new different ways and re evaluated them. Each time I learned something new.

Ratios can help to make a stock solution, dose on the leaner side, but you really run into issues with traces and if you provide continuous non limiting external ppm's of nutrients. Then ratios really do not apply well.
And in most cases, for us anyway, the ratios are all over. Some like to play with them and balance them, test etc.
Most don't.

However, if you are going to discuss ratios, make them something you pay attention to, test them etc......at least understand them well enough and see what they really mean :thumbsup: 

FYI, in CA, most of the soils here in wetlands are N limited, not P limited based on ratios and tissue content. Plants do very well. 

Regards, 
Tom Barr


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## vance71975 (Jun 4, 2008)

plantbrain said:


> I've had a dozen or more discussions over this silly mistake.
> Hopefully more folks will not make the same mistake in the process.
> 
> Redfield ratio is just that, it is *not a mass based ratio*, nothing is weighed, there are no ppm's, no mg/l involved with the RR. I have no idea why folks have done this, but it keeps getting promoted and the myth only gets worse.
> ...



ummmm can you say that again only this time in English? After reading this i REALLY REALLY feel stupid cause i cant make any sense out of any of what you just said! i got to ask are you a Rocket Scientist or a Physicist?


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## plantbrain (Dec 15, 2003)

vance71975 said:


> ummmm can you say that again only this time in English? After reading this i REALLY REALLY feel stupid cause i cant make any sense out of any of what you just said! i got to ask are you a Rocket Scientist or a Physicist?


It is in English. It's worded specifically.

Look up what the Redfield ratio is.
Then see how it was used to make a dosing routine for aquatic plants.

I add say 7 ppm of N and 1 ppm of P(or 14 ppm of N and 2ppm of P- same ratio) for my routine.

These links show folks who do not understand the difference between the no# of atoms vs the specific weight of the atoms.

Aquarist do not think to dose in terms of atoms, we dose in terms of weight of the nutrients to get mg/l or ppms. They did not take that in to account and thus are 2.2 x off in their calculation.

If the topic is outside your understanding that is fine.
I did not give a hoot about PMDD when I first saw it either.
Or dosing ppms of NO3 etc.
Such talk turns many off.
Nothing wrong with that either.
I decided to learn more about it and went from there.

If I can learn, so can anyone.
Initially, it all sounded weird to me and was above my head.
Same way if I walked into a fine Art's class and tried to paint and discuss it.
It'd look pretty bad, but over time if I was interested in it, I'd get better. 

But what we learn is not inherent and innate, we have to do the work to learn , workout to train for a marathon etc and make mistakes. I had to to get a better understanding and teach myself/learn from others.

Regards, 
Tom Barr


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