# Confused. Ratio vs ratio



## Andi (Feb 6, 2008)

I've been reading various literature that focuses on aquatic plants. Some aquarium and some pond. Repeatedly I come across that there needs to be 7 atoms of nitrogen for each phosphorus atom. That ratio makes sense. Where I get confused is in the recommended fert ratio in the same literature (pond and aquarium) is even (eg: 6-6-6 or 10-10-10).
Can anyone shed some light on this?


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## TarantulaGuy (Apr 15, 2009)

Are you talking about the redfield ratio?


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## niko (Jan 28, 2004)

You will find all sorts of articles and posts about what ratios of what chemicals your plants need. Very much every single piece of information will either try to somehow sell you something or serves a personal agenda. If someone doesn't tell you it's easy to buy into the information because it is made to make sense.

The following is a very easy to read and easy to understand article. Get these basics right and go from there. You will see that every single piece of information out there uses the same principles in one form or another. Understand the main points and do not get into tiny details. An aquarium does not work based on numbers alone but using numbers sets a general trend.

http://buddendo.home.xs4all.nl/aquarium/redfield_eng.htm

A word of caution - note what exactly the article you are reading talks about. Phosphorus(P) and Orthophosphate (PO4) are not the same thing. Nitrogen (N) and Nitrate(NO3) are not the same. Don't confuse simple things like that.


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## BruceF (Aug 5, 2011)

Aquarium Chemistry: Phosphate And Math: Yes You Need To Understand Both

By Randy Holmes-Farley, Ph.D.

http://www.advancedaquarist.com/2012/3/chemistry


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## Andi (Feb 6, 2008)

The few different places I read that a plant needs 7 atom of nitrogen for each atom of phosphorus made no mention of the Redfield Ratio, which is 16:1. The 7:1 ratio was referring to what plants need for taking up nutrients, not the ratio that will keep algae at bay or grow coral. Eg: If a plant has 6 atoms of nitrogen and 1 atom of phosphorus it can't take up either, as well as the reciprical of 7 atoms of nitrogen to no atoms of phosphorus. One of the sources that I know of for sure is _Encyclopedia of Water Garden Plants by Greg and Sue Speichert_. I worked for Greg about 15 years ago. He was a horticulturist. I'd ask him directly but he passed away 2 years ago. I have no idea where Sue is, or if she would even know for sure. I've also read this same 7:1 ratio referring to aquarium plants, but I can't recall the exact source.

BTW, thank-you for the links, for me and others who may be interested as well.


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## niko (Jan 28, 2004)

You are getting into too much math. In an aquarium is impossible to maintain exact concentrations of fertilizers. And algae are always waiting to step in. So between those two things we have found approaches that work. But nothing works 100%.

You will find two main approaches:

1. Load your water with everything you plants need.
The idea here is that if the plants have everything they need they will outcompete algae.
Problem is people drop the ball and don't realize it - their CO2 is not high enough, their biofilter does not work properly, there are organics in what looks like a perfectly clean tank, etc.

2. Use rich substrate + water that is void of nutrients (but they are added in tiny amounts on a daily basis)
The idea is that N is in excess in the substrate, the substrate has an ability to suck Phosphate and other nutrients too. The water is kept intentionally clean of nutrients but they are added in small amounts to keep the substrate full of nutrients and to feed whatever plants find it easier to eat from their leaves.
Problems are organics, small biofilters, lack of clear information how that approach works.

If you execute both approaches perfectly you will have a clean and healthy tank. Read the above again and decide for yourself which approach provides less risk for algae to grow. The answer is obvious but many people don't acknowledge it.


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## Yo-han (Oct 15, 2010)

As Niko said, your making it too much of a science. Unless you know exactly how much NPK is in your food, and you know how much N is gassed off as N2 etc., this is all impossible to maintain. The ratio plants need also differs from specie to specie. Just make sure your plants have plenty of all, whether you supply it by a rich substrate or a rich water column.


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## Zapins (Jul 28, 2004)

I posted a long response to this question the other day but due to the double post issue we've been having my reply was deleted when I removed the double post... -.-

Anyway, here is an abbreviated version of what I wrote.

Without seeing the article the 7 atoms of N to 1 of PO4 sounds like a transporter ratio. Basically there are proteins that only work if there are a certain number of atoms of a certain kind in them, so for example in this picture you see that the protein NHE-2 only works when there is one atom of Na outside and one H inside. If there are no H atoms to exit the cell then no Na can be brought in even if there are a million atoms outside. Perhaps that is what the article is talking about.










The other part of your question is the 6-6-6 part. When they say 6-6-6 they are talking about a ratio of N-P-K that the plant likes best. Not all plants use NPK at the exact same rate. For example some plants (like azolla and marselia) need less nitrate fertilizer addition since they can nitrogen fix using bacteria in their roots, so an appropriate fertilizer formula would have low nitrogen content something like 1-6-6. Another example is some plants have larger root systems than others so they need to make more protein than other plants with smaller root systems, since nitrogen is used to make proteins these plants will need more nitrogen than other plants like epiphites (amazon sword vs. anubias or moss). Each plant's nutritional needs are different based on their growth patterns, but they all use the same transporter proteins. So even though the moss needs less nitrogen fertilizer addition to grow it still takes it up in a 7:1 ratio.


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## Andi (Feb 6, 2008)

Thank-you for your explanations. Sorry it took so long to get respond. I have a better understanding now.


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