Dosing Iron and Phosphate at same time? - The Planted Tank Forum
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post #1 of 21 (permalink) Old 10-09-2016, 02:22 AM Thread Starter
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Dosing Iron and Phosphate at same time?

I have always been told, both in print and in person, that it is a bad idea to dose our tanks with micros at the same time we are dosing macros. This is said to be because the iron and phosphate will combine to form insoluble iron phosphate, which will not be available to the plants. However, I also know that the metal micronutrients, like iron and copper, are always in a chelated form in the fertilizer mixes we use, like CSM+B. I believe that chelated iron will not combine with phosphates - that is a primary reason it is chelated. "Metal chelate compounds are common components of fertilizers to provide micronutrients. These micronutrients (manganese, iron, zinc, copper) are required for the health of the plants. Most fertilizers contain phosphate salts that, in the absence of chelating agents, typically convert these metal ions into insoluble solids that are of no nutritional value to the plants. EDTA is the typical chelating agent that keeps these metal ions in a soluble form." (https://en.wikipedia.org/wiki/Chelation not the best source, but it is what I found on Google.)

Which is correct? If I dose CSM+B and KH2PO4 at the same time do they form iron phosphate, or does the chelator protect the iron from the phosphate?

A second warning we all get is that we can't make a liquid mix of all of the needed ferts, NPK and trace elements, which include iron, for the same reason. Is this true? Does the chelator also protect the iron from the phosphate in the much higher concentrated mix in a liquid fertilizer? Does anyone have a link to an authoritative discussion of this?

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post #2 of 21 (permalink) Old 10-09-2016, 02:33 AM
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Hi Hoppy,

Interesting question....got a test tube?

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post #3 of 21 (permalink) Old 10-09-2016, 03:05 AM Thread Starter
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The easy test would be to use a litre of water, add about 5 ppm of KH2PO4 and about twice that volume of CSM+B, shake it up and test for phosphate. Then let it sit for one day and retest. But, I don't have a phosphate test kit, nor do I want one. I don't know any good way to test the higher concentration that comes with a liquid fert mix. And, this would need to be done with varied pH of the water, since chelators are effective over different pH ranges. I'm hoping someone has already done this.

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post #4 of 21 (permalink) Old 10-09-2016, 07:15 AM
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Seems iron & other base metals have a high ability to store Phosphates,therefore dosing both @ the same time would only lock your P dose into the minerals?
heavy reading here on mine tailing & P absorbtion.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4546615/
If you can come up with good keywords for searching enter that in upper RH corner of that page to start new query.
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post #5 of 21 (permalink) Old 10-09-2016, 04:22 PM Thread Starter
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Seems iron & other base metals have a high ability to store Phosphates,therefore dosing both @ the same time would only lock your P dose into the minerals?
heavy reading here on mine tailing & P absorbtion.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4546615/
If you can come up with good keywords for searching enter that in upper RH corner of that page to start new query.
There is no question that phosphates can combine easily with iron which is not chelated. My question is about the chelated iron, and other metal micros, in trace element mixes, like CSM+B. I believe that bacteria serve the same function as chelators in nature, keeping some iron available to plants. I'm wondering if the reason for not dosing micros and phosphate together is that the common chelators used in trace mixes are not effective over a wide enough pH range to allow that.

I have no bone to pick with this - I'm just trying to broaden my knowledge base.

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post #6 of 21 (permalink) Old 10-09-2016, 05:06 PM
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Hoppy, this is a question I wish I asked a long time ago. For my tanks, I dose PPS-Pro. And with this system (assuming I understand it correctly), I dose XX amount of micros and XX amount of macros EVERY day. I don't remember if there is some time reference between micro and macro dosing, but, in my weekly life I would not have time to wait XX hours between micro and macro dosing. Would seem to me, if PPS Pro is an acceptable system and it includes dosing CSM-B as well as KH2P04, then I can only naively assume the CSM-B chelator will protect the iron from the phosphate. Can I dose Macro and Micro at the same time? Yes, simply dose both at the same time into moving water. Text from this site.

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post #7 of 21 (permalink) Old 10-09-2016, 08:17 PM Thread Starter
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If we can dose all of our ferts at one time, why can't we make a liquid mix of all of those ferts and only dose that one liquid? Obviously in a liquid mix the concentration of both iron and phosphates is very much higher than in the aquarium water, but with that is a very much higher concentration of the chelator, too. Is it just a "be on the safe side" issue?

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post #8 of 21 (permalink) Old 10-09-2016, 08:50 PM
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Chelated iron forms should be fine. Chelated irons need to be suspended at all times. Agitated. We use a saying called WALE

W. Wettables
A. Agitate
L. Liquids
E. Emulisifade concentrates

Chelated iron most be suspended at all times. Benefits all plant material. Over dose is hard to do. But a temporary blackening effect.

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post #9 of 21 (permalink) Old 10-09-2016, 08:59 PM Thread Starter
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Does this mean chelated iron is not dissolved in the water, just in suspension? My mix of water and CSM+B starts out very clear, and remains so for a week or so, then begins to get a bit cloudy. Is that because the bond between chelator and iron cation is being broken?

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post #10 of 21 (permalink) Old 10-09-2016, 09:32 PM
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Quote:
Originally Posted by Hoppy View Post
... Obviously in a liquid mix the concentration of both iron and phosphates is very much higher than in the aquarium water,...
Couple points against mixing and storing them:
1. Chemical reaction runs faster at higher concentration. In the aquarium at lower concentration, the plants still have opportunity to intake before iron and phosphates completely form insoluble substances.
2. When storing liquid mix longer, iron and phosphates can completely form insoluble substances before they are dosed.
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post #11 of 21 (permalink) Old 10-09-2016, 10:41 PM
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@max88, your response would explain why dosing is OK, but mixing is not.


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post #12 of 21 (permalink) Old 10-09-2016, 10:42 PM Thread Starter
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Originally Posted by max88 View Post
Couple points against mixing and storing them:
1. Chemical reaction runs faster at higher concentration. In the aquarium at lower concentration, the plants still have opportunity to intake before iron and phosphates completely form insoluble substances.
2. When storing liquid mix longer, iron and phosphates can completely form insoluble substances before they are dosed.
Therefore, chelators reduce the forming of compounds with phosphate, but don't eliminate them. So, solutions lose bioavailable iron slowly, if the concentrations are low, but much more rapidly with high concentrations.

Another possible factor is that organic compounds - chelators, for example - are not nearly as stable as inorganic compounds, so over time the chelators break down?

Is the color change of my CSM+B + water dosing solution over time, from clear green to cloudy brown, a sign that the chelators are losing their effectiveness? If so, then I need to refrigerate my CSM+B dosing solution, or make less at one time and use it faster.

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post #13 of 21 (permalink) Old 10-09-2016, 10:52 PM
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Curious Hoppy, I am mixing around 5 grams CSM+B into 500mL distilled water. This gives me a light brown colored water. I dose 1mL per 10 gallons (same dosing as original PPS-Pro, just less micros).
Near as I can tell the color of the CSM+B mix stays the same until I run out. But then again, I guess I never really paid attention.

Is your mix concentration about the same as mine? Is CSM+B always the same regardless of brand (who you buy it from)? Or is it possible one brand has more / better / different chelators? (I really hope not)


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post #14 of 21 (permalink) Old 10-09-2016, 11:12 PM
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The white cloud you see is just mould, has nothing to do with chelators. You can prevent this by using Nipagin, potassium sorbate,..
I mix my own complete fertilizer and use, beside other elements, about 6 gram of potassium phosfate and 12 gram of Fe DTPA and EDDHMA per liter. As long as you keep the chelator intact nothing wil percipitate. I do this by keeping the pH around 4-5, and keeping it dark and cool. Have a control bottle in the fridge for about 2 years now and all is still in solution.
In my dosing pumps I use a mix of macro's on one channel, and micro's with gluconate as one of the Fe chelator on another. If I mix these 2 together I get instant percipitation.
So dosing phosfate and Iron on the same time had a lot to do with the chelator that is used. A chelator that will break down fast can bind with the phosfate.
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post #15 of 21 (permalink) Old 10-09-2016, 11:34 PM
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Chelated iron in water should darken over time if left alone. Over long periods of time it seperates. Iron has low persistence in all plant material. Hence why its constantly applied and like our algae discussions. We (people) want things super green or certain aquatic plants super red. When in nature often times they are not that green or red.
Many people including myself have talked about finding and understanding the balance of what a healthy and or natural aquarium is.


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