# Do not dose PO4 and fe together......A MYTH??????



## Glouglou (Feb 21, 2006)

I was explaining my concern about dosing Iron and Phosphate on a french canadian forum when I was challenged to bring some scientific evidence about it.
• I hear somewhere that the phosphate will bound with the iron and precipitate out of the solution and bla! bla!...
and you probably hear that to.

After some research on the web, I was left with little evidence of my knowledge and come across 2 devastating article on the bioavailabality of iron that change my concept of a fair world forever

The first article tell my ignorant myself:

*whatever form iron take chelated, ferrous or ferric it will always be retransform and finally be used by plants....*



> So the iron can be gotten by the plants (eventually),
> sooner or later, regardless of whether it's about the tank
> as chelated, ferrous, or ferric? If you dose it, they can
> use it


http://fins.actwin.com/aquatic-plants/month.200304/msg00022.html

*Now, the next one is stunning!*

Here,* if I understand well... *, the phosphate combine two quality in interaction with iron that go against every knowledge I have on the matter...



> Ferrous iron is soluble as a cation, ferric iron is not. However, ferric iron can form soluble complexes with many inorganic and organic ligands
> 
> and more......
> 
> ...


http://2the4.net/iron.htm

*1- Phosphate can complexed ferrous iron to keep it available longer, like a chelating agent do. It will oxidized more slowly in ferric (non-soluble form)*

*2- Even in is ferric form, the complexing agents like humic acid and phosphate will combine with the ferric form and give back some solubility*

*I need Help to understand this one...*

:brick:


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## scitz (Mar 16, 2004)

I wouldn't mix PO4 and a trace element mix up in the same bottle as this will cause problems in the form of a precipitate. You don't want this happening in a bottle of solution, whether this precipiate is an unusable to plants form or not. It just ruins the solution.

This one has pretty much been proven as myth by at least anecdotal evidence. Same way that the MythBusters shows don't scientifically prove those myths aren't true. (editors note: fun show to watch all the same)

I dose seperately, macros on one day and micros the next. I use the EI methodology, btw. So its 1/8 tsp of each KNO3 and K2SO4, one dropper full of KPO4 solution monday and thursday. And a hit of CSM+B trace element mix on tuesday and friday. 50% or higher water change on sunday.

I have skipped days and dosed both macro and micro on the same day at least once a month and haven't noticed any ill effects. I have also mixed 1/32 tsp of CSM and 1/32 tsp of KPO4 in 50ml of water each until dissolved and mixed them together and got a whitish precipitate that didn't like to dissolve in 250ml of clean water without heat and vigorous stirring. Your Milage My Vary.


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## Glouglou (Feb 21, 2006)

*Thanks Scitz!*

Well, ,it was just a hit to see how important is to go deeper in any subject proposed. One day, we know, and the other we don't...
It show how important it is to keep an open mind to be able to acquire any knowledge that anyway can be challenge tomorrow!

Even in aquaria, major philosophic lesson can arise.

EUREKA:bathbaby:

KNOW I KNOW (until tomorrow) that phosphate can help keep all the form of iron available to plant!


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## Mjproost (Nov 17, 2005)

I am by no means a chemist, or aquatic expert. I understand Iron will eventually restransform and be available to the plants, but how long will it take and how much will be available? 

I too have dosed FE and PO4 at the same a few times without ill-effects in the short term. But, I have never tried at high levels and I would never mix the two in the same solution. I always try to err on the side of caution and not dose them at the same time. Every other day EI method works best for me and just seems safer. I say why risk it?


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## Avalon (Mar 7, 2005)

Before the branding of the "EI" method, I dosed ferts every other day, macros and micros together. Never had a problem. I don't mix the ferts up beforehand. I like them to be stored and dosed separately (personal preference).


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## Bert H (Mar 2, 2004)

The precipitated product also is available to the plants, but they must take it up through their roots. It is my understanding, that the uptake from the water column for this is much easier than through the roots. Any chemists care to comment?


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## Glouglou (Feb 21, 2006)

*To MjProost*

You get in the 2 web address I post before very interesting stuff. Anyway they open some light on the subject.
 
From the first address:
http://fins.actwin.com/aquatic-plant.../msg00022.html

This is the complete text without the finale I already quote before...



> Light breaks down ferric-edta (and other ferric chelates) through a reaction called photoreduction. Photoreduction is one of the major pathways by which iron can get wrestled out of a strong complex like ferric-edta. When ferric-edta is broken down by photoreduction the chelating ligand is oxidized and the iron is reduced and released into the water as ferrous iron, not as ferric iron.
> The ferrous iron will remain in solution for a while until it is taken up, oxidized back to ferric iron and/or recomplexed possibly by another chelating ligand and possibly by hydroxide or other common ligands in the water.


If I understand well, the chelated iron we use in aquaria is a ferric-edta (or chelated), meaning that it is complexed by any chelating ligand (edta, Humic acid, fulvic acid and tannic acid. Phosphate also serves as a very effective complexing agent for iron.
This is too keep it longer in solution to be available by the plant in the ferrous form. Everyting that is not used up by the plant is oxydized back in ferric form and this ferric form will be recomplexed with any other ligand in solutions to be I guess release again in his ferrous form in a cycle...

Note: In the second link they talk about:

http://2the4.net/iron.htm



> t is important to remember that complexed ions typically react more slowly than uncomplexed ions. This impacts the behavior of ferrous iron. Ferrous iron normally can be oxidized to ferric iron in minutes (see below for more details). Complexed ferrous iron may take months to complete the same reaction. This has profound implications for the fouling of groundwater injection systems.


*Interesting points*
• Here they say that you can have a complexed ferrous iron (maybe this is the stuff we have in aquaria)
• another point is that complexed iron always take longer to react.

The next interesting quote is the time ferrous iron stay in this form.
(in the second link) is about iron oxydation:


> IRON OXIDATION
> 
> The time required for uncomplexed ferrous iron to undergo oxidation to the ferric state is dependent on many factors, the dominant being: pH; temperature; dissolved oxygen level; and the presence of other soluble ions. The lower the pH and temperature the longer the time required for completion of the oxidation reaction. Increasing dissolved oxygen decreases the time required for oxidation. For example:
> 
> ...


Some things to think about...


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## BryceM (Nov 6, 2005)

My take on the whole thing is this........

I think all the hype about this started when people tried to mix up highly concentrated solutions containing all their necessary ferts. In this situation, PO4 and Fe can precipitate and leave solution. The gunk then sits on the bottom of the bottle and never makes it into the tank. This then leads to nutrient deficiencies and the whole concept quickly morphs into internet gospel.

If you look at the more ordinary situation of an aquarium sitting there, day in and day out, both phosphate and iron co-exist in a very dilute solution and are always available in the water column. Adding a little phosphate doesn't immediately cause all the iron in the water to precipitate out and fall to the substrate.

Do I have the numbers to back this up? No, but dilute solutes can co-exist without precipitating out of solution. In an aquarium, almost every important solute is enormously far away from its saturation point. We're talking about parts per million. Concentrations in a stock solution are orders of magnitude higher.


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## mrbelvedere138 (Jan 18, 2006)

I put all my ferts in one bottle to dose the shrimp tank. It's easier that way. The solution turns cloudy and thick, which I assume is the phosphate reaction, but a hell of a shaking before I dose seems to work out just fine.


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