# Iron phosphate



## Soilwork (18 Oct 2017)

What ratio does iron and phosphate bind at?

If I was to add equal amounts of Fe and po4 ions in to RO water would there be any of any of the ions left over?


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## dw1305 (18 Oct 2017)

Hi all,





Soilwork said:


> What ratio does iron and phosphate bind at?


It is FePO4.nH2O, so one Fe+++ to one PO4---. 

It isn't quite as straightforward because it depends <"which other ions are in solution">. The least soluble compound will form first, which is why you can add <"ferric chloride (FeCl3) to waste water"> and mop up any PO4--- ions (precipitated as iron phosphate).

cheers Darrel


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## Soilwork (18 Oct 2017)

Do you think that dosing FeSo4 is worthwhile in EI situations where po4 is abundant? What about other forms of iron? What is to stop iron that is bound to EDTA immediately binding with excess po4 once the edta complex is broken? 

What if the other way round? Too much iron depleting lower amounts of po4 due to precipitation?


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## dw1305 (19 Oct 2017)

Hi all, 





Soilwork said:


> What is to stop iron that is bound to EDTA immediately binding with excess po4 once the edta complex is broken?


That is pretty much it, as soon as the Fe+++ ions become available they will form new (mainly insoluble) compounds, if they aren't taken up by a plant. You can keep the iron ions in solution in acidic conditions, but as you approach pH7 (or have a lot of PO4--- ions in solution) insoluble compounds will form. 





Soilwork said:


> Do you think that dosing FeSo4 is worthwhile in EI situations where po4 is abundant?


No, it is just going to precipitate out of solution. Because iron is reactive, and most of its <"compounds are insoluble">, it is always going to be difficult to keep in solution.





If you have acidic tank water then you can add iron as iron sulphate, but even in acidic conditions, if you have a lot of PO4--- ions present, then insoluble iron phosphate complexes will form.




Chelators work because plants don't need much iron (it is a micro-element) and they intercept enough, of this constant trickle of Fe+++ ions, before they become unavailable. 





Soilwork said:


> What if the other way round? Too much iron depleting lower amounts of po4 due to precipitation?


This is how "phosphate strippers" in waste water treatment etc work.  This is from <"Wastewater treatment: Tackling phosphate removal">





> ....To reduce phosphate additions in the discharge to water courses from sewage treatment works, the sewage is treated with iron salts, which are converted to insoluble ferric phosphate; the phosphate is removed by the DynaSand® vertical sand filters, settled in primary settlement tanks, further treated and used on farmland......


cheers Darrel


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## Soilwork (19 Oct 2017)

Thanks Darrel.  I know Clive is just going to say stop worrying about this and add more of everything but I just don’t want to add more and get more precipitation.

It’s probably better to keep phosphates in solution and iron in the substrate then ideally.  I don’t know how quick the reactions occur compared to plant uptake.  Obviously they will get some and as you rightly point out iron is a micro nutrient after all.  My main concern is that I’m finding I’m having to increase iron dosages to stop plants yellowing but fear I am just precipitating both fe and po4.

Lastly if there are more reactive ions than Fe (K+, Mg) why do we only talk about FePo4 and Capo4?


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## dw1305 (19 Oct 2017)

Hi all, 





Soilwork said:


> It’s probably better to keep phosphates in solution and iron in the substrate then ideally.


Things are slightly different in the substrate, where iron may be come available in the zones of fluctuating REDOX that occur around plant roots (the rhizosphere) and near to the substrate surface.

To some degree the same applies to the insoluble  phosphorus compounds that have sunk to the substrate, they may become available again as pH and oxidation states change, additionally any PO4--- ions that have been bound to clay minerals  and humus (with anion exchange capacity) may become plant available, although because the PO4--- ion has a high valency (the three negative charges) they are likely to remain bound.





Soilwork said:


> Lastly if there are more reactive ions than Fe (K+, Mg) why do we only talk about FePo4 and Capo4?


It is down to the solubility. There is a useful <"solubility chart on Wikipedia">.

We know that potassium di-hydrogen phosphate (KH2PO4) and di-potassium hydrogen phosphate (K2HPO4, solubility 226g/1000cm H2O) are soluble because they are used as fertilizers in EI, but once we are away from the alkali metals, then nearly all phosphates are insoluble.

Ca3(PO4)2 <"Ksp"> = 22.07×10-33
FePO4.2H2O Ksp =  9.91×10-16
Mg3(PO4)2 Ksp = 21.04×10-24

Magnesium phosphate (Mg3(PO4)2) is insoluble (more insoluble than iron phosphate, but less insoluble than calcium phosphate) so if you had a lot of magnesium ions (Mg++) in solution they would precipitate out any PO4--- ions, but only if you had already exhausted the supply of Ca++ ions.

Reactivity is useful in finding out whether you are likely to have problems with insolubility. You can find elemental gold (Au) and Platinum (Pt) because they aren't reactive at all (don't form compounds) and conversely it is really difficult to keep the <"alkai metals"> as elements (you have to store them under oil to stop them oxidizing, or forming hydroxides, in air or water)  all the other metals lie some-where in the middle.

cheers Darrel


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## Soilwork (19 Oct 2017)

Ok so are you saying that, unless the conditions are optimal, the PO4 ions that are bound to my high CEC substrate (Eco Complete) are less likely to be 'given up' for plants because they are so tightly bound?  What does this mean in terms of adding PO4?  Could this be _one_ of the reasons that people report better growth rates when adding large amounts of PO4, the fact that the likelihood of plant uptake is increased increased opposed to the actual concentration added?

A couple of weeks ago i mistakenly added around 90ppm of Calcium from calcium chloride.  It sounds as though this would have most certainly precipitated any PO4 I had in solution.  That is without taking in to account the high amounts of Magnesium and Fe i already had in solution.  Perhaps i need to add much more PO4 to counteract this?

My tap water alone has 10x the amount of Calcium than it does phosphates.  Perhaps there is an issue here too?

On the flip side, if i increase PO4 dosing I don't want to increase the probability of iron precipitation either.  I am trying to think of ways to maximise the addition of my fertilisers to avoid precipitation based deficiencies.  

I have a lot of GSA on my glass which is said to be an indication of low PO4 however, even after halving my PAR the GSA still forms.  Perhaps i have a po4 issue here?

In my soil tank, things only really began to take off when (along with some other changes) i stoopped adding iron, calcium and magnesium and left these things to the soil.  However i carried on with EI values of NPK.  I had lots of red clay in a deep soil substrates and as i understand it the John innes no3 soil is nicely limed and most likely contained plenty of Mg and Ca.


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## dw1305 (19 Oct 2017)

Hi all,





Soilwork said:


> Could this be _one_ of the reasons that people report better growth rates when adding large amounts of PO4, the fact that the likelihood of plant uptake is increased increased opposed to the actual concentration added?


Quite likely, the <"plant available phosphorus"> will be a small fraction of the total phosphorus reservoir. 





Soilwork said:


> I have a lot of GSA on my glass which is said to be an indication of low PO4 however, even after halving my PAR the GSA still forms. Perhaps i have a po4 issue here?


It is really difficult to tell, as you probably gathered from this thread nutrient issues aren't always a simple case of how much you've added. 





Soilwork said:


> In my soil tank, things only really began to take off when (along with some other changes) i stoopped adding iron, calcium and magnesium and left these things to the soil. However i carried on with EI values of NPK. I had lots of red clay in a deep soil substrates and as i understand it the John innes no3 soil is nicely limed and most likely contained plenty of Mg and Ca.


 My suspicion would be that you should have plenty of everything, a conductivity reading would be interesting. 

But I really don't know, I run my tanks nutrient depleted with fairly soft water, so I don't really have much experience of harder water and higher nutrients, and none of the tanks has GSA. 

When we did more work with waste water the plastic gutters used to get pretty furred up, but I don't know whether any of that was GSA or not.

cheers Darrel


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## ceg4048 (19 Oct 2017)

Soilwork said:


> On the flip side, if i increase PO4 dosing I don't want to increase the probability of iron precipitation either. I am trying to think of ways to maximise the addition of my fertilisers to avoid precipitation based deficiencies.


Trying to micromanage nutrients is not the best strategy. All the hand wringing about what precipitates is simply wasted energy.

So the first thing to consider is that if you have calcium in your tap there is absolutely no need to add more calcium. So now you've just created a new problem for yourself.

Calcium, like most micronutrients, accumulates it's concentration in the leaves since they are mostly immobile. So even if the water is poor in calcium, at some point they will be sufficient levels accumulated. You really never need to worry about calcium deficiency.

When you add iron, it should always be on alternate days from when you add NPK. This is the primary method to avoid Iron Phosphate precipitate.
Barr's data indicates that when you add Fe, the plants uptake for about and hour and after that uptakes shuts down. Micronutrient uptake is self regulating. So it doesn't really matter how much Fe precipitates out of solution after that first hour.

GSA does not automatically go away just because you have reduced the lighting and increased PO4, especially if it's on the glass. Scrape it away using a razor blade. As long as it is not on the leaves then this is a partial victory. Continue to add a little more PO4 and carry on. Also remember that GSA is triggered by any combination of low PO4/CO2, not only low PO4.

If you're dosing EI levels of traces and NPK and are still getting nutrient related symptoms on the leaves then this is an indication that flow/distribution should be examined. When you get yellowing or paleness of leave, be care to note whether this occurs on all the leaves (mature as well as young) or just on young leaves. If it occurs just on the young then this confirms a micronutrient issue. If it occurs on the mature leaves or unilaterally then this is a most likely a Nitrogen issue.

Cheers,


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## Soilwork (20 Oct 2017)

Ok thanks.  It does appear to be mainly on the older leaves, most of which are actually still emersed leaves.  I have not been strict enough with keeping to EI in terms of dosing so I am starting as of today.  I did a 75% water change last night and this morning i dosed my EI macro mix.  Tomorrow will be micros etc.  

I am currently dosing my Magnesium with the NPK.  If we are talking about separating Phosphates and Iron would there be any value in putting the magnesium in to the micro mix to prevent any possible Mg+Po4 precipitation or am i being too pedantic again?

My Co2 seems to be good.  I know snails are not generally a fan of high co2 anyway so this may not be a good indicator but they only seem to come down from around the top of the tank to graze after the CO2 has gone off.  I also believe my flow is OK but if my proper attempt at EI fails i will start looking in to these two aspects.

Regards
CJ


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## ceg4048 (21 Oct 2017)

Soilwork said:


> I am currently dosing my Magnesium with the NPK. If we are talking about separating Phosphates and Iron would there be any value in putting the magnesium in to the micro mix to prevent any possible Mg+Po4 precipitation or am i being too pedantic again?


Yes, you are being pedantic. It will be the death of you. Death by pedantic is the second most common occurrence in The Matrix. The most common, of course, is death by test kit.
Dose Epsom Salt whenever it is most convenient.



Soilwork said:


> I have not been strict enough with keeping to EI in terms of dosing so I am starting as of today. I did a 75% water change last night and this morning i dosed my EI macro mix. Tomorrow will be micros etc.


OK, well, that's a good start. I'm never sure why folks feel that dosing is a matter of strictness. You're only dosing 5 of the 7 days a week. Surely you visit the tank 5 times a week or more? How often do you feed the fish? Is this considered strictness or fun? If it helps the psychology maybe dose at the same time that you feed.

I guess maybe I'm such a fanatic that I don't even think about it. I just dose automatically. Every morning i get up, examine the tank, remove any dead or dying leaves, Shake the stems to dislodge accumulated dirt, then dose. It's just an automated tank maintenance procedure. Perhaps if you do this often enough it will become habitual.

Cheers,


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## Soilwork (21 Oct 2017)

I suppose it’s a case of the more your habits provide results the more you follow them but I worry that much about having too much ferts in my tank (not because of algae or fish health) but because it just feels like pollution even when I know it works so I end up skipping a day here and there, or i get home late and think there’s no value at the end of the photoperiod.  So then I end up typing ‘plants feed at night UKAPs’ in to google and find out they take nutrients in 24/7 so it’s just overcoming these obstacles. 

I also need to bin my tests kits.

Feeding plants whilst feeding fish sounds like a great idea. 

Cheers
CJ


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## Soilwork (23 Oct 2017)

Clive, I’m curios, do you use any form of glutaradehyde?


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## ceg4048 (23 Oct 2017)

Yes, I have done, but it is very expensive on a large tank. I have used Excel, Easycarbo.

If you have very high lighting and you don't want to push the CO2 too high for the sake of the fauna then you can easily supplement with daily liquid carbon.

Also, if you suffer a CO2 related algal bloom, you can suppress the bloom with the liquid while you fix the problem.

In the old days, if a BBA bloom arose, it was extremely difficult and time consuming to get rid of the tufts, even when you fixed the cause.
The liquids make it easier to evict the blooms while you work on a solution. 
The liquid is a good tool to have in your box.

Cheers,


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## Soilwork (23 Oct 2017)

Thanks for the reply.  I noticed better plant health when using it but at the same time I don’t want to be reliant on it.  I’d like to have the technique at hand to be able to use just the gas.

My drop checker is green and my nerites hang out around the surface until co2 goes out then they come down to graze.  I don’t know if this is saying I have too much co2 or my flow is incorrect etc but the differences when using easycarbo can clearly be seen.

I wonder whether the plant leaves needed a helping hand by thinning out the periphyton layer maximising nutrients and co2 uptake and that is exactly what the easycarbo is doing. 

I was told during a Facebook conversation the other day that glut provided a very very small amount of carbon and then they went on to derive a final co2 comparison ie X amount of glut is = to this amount of co2.  I thought this calculation was almost impossible to extrapolate with any degree of accuracy?  To try and avoid an internet war I continued to let them entertain the masses with their knowledge.

Anywho I just hope using this is not seen as cop out for not being able to manage co2.

Having said that I did do a 75% water change a few days ago, maybe that has had something to do with the resurgence in plant growth.  I’m a bout to do another. 

Cheers

CJ


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## ceg4048 (23 Oct 2017)

No, I don't think it's a cop out. As I mentioned, it's just another tool. I don't see how anyone could determine numbers for comparison. In any case it's more important to know, for those that use only the liquid, that the liquid is not as effective by itself as gas. No one actually knows how much gas is dissolved or how much gas is available, so any calculation is pure fantasy.

Inverts trying to escape does indicate that there is a lot of gas. I don't like snails and that's how I get rid of them. Inverts are typically less tolerant to gas than fish are so it's not all that surprising.

Sometimes there is so much light that the amount of gas needed to satisfy their needs is too much for the fauna.
That's just the way it is, so the best we can do is to have the best distribution and most efficient dissolution methods we can.

Cheers,


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