Dosing Iron to reduce Phosphates?

[Randy Holmes-Farley Verified Community Expert]

So that is why my phosphates are dropping, Ever since I started dosing iron. Now I have to dose phosphate so it does not drop to zero. Phosphate levels have been 0.12-0.06 for several years, now drops to 23, 17, now 13.

I doubt it, unless you are intentionally dosing unusually large amounts of iron. I do not think this is the cause of low phosphate.

Let's look...

A typical dose of iron (my dose; see below) is, say, 2 ug/L. How much phosphate could that remove even if it ALL became ferric phosphate?

FePO4 is about 1/3 iron and 2/3 phosphate by weight.

So 2 ug/L of iron might combine with 4 ug/L of phosphate, or 0.004 ppm.

Typical foods daily add 0.02 to 0.3 ppm per day:
https://reefs.com/magazine/aquarium-chemistry-phosphate-and-math-yes-you-need-to-understand-both/
Thus, if you dose iron at my done once a week, you are only possibly precipitating 0.004 ppm out of a weekly food addition of 0.14 to 2.1 ppm of phosphate, or only 0.2% to 3% of the total phosphate.


This is from my Triton testing article:

Iron (Fe). The natural iron level varies a lot with depth, but surface seawater may have only 0.006 µg/L. The Triton LOD = 0.3 µg/L. I dose iron, and when I dose it I boost iron to roughly 1-2 µg/L, which would be detectable. This sample was taken more than a week after the last iron dosing, and none was detected as it gets depleted in the meanwhile. I’ve not yet seen a Triton test result for a real aquarium sample that had detectable iron, but that doesn’t mean these tanks are necessarily deficient. Iron is also a case where the form is critical, and ICP cannot distinguish form. Binding to organic matter, for example, can alter the bioavailability of iron.

 

[Randy Holmes-Farley Verified Community Expert]

So that is why my phosphates are dropping, Ever since I started dosing iron.

More likely, IMO, is the phosphate has spurred the growth of photosynthetic organisms such as micro algae, microalgae, corals, etc.

 

[anthonygf]

I doubt it, unless you are intentionally dosing unusually large amounts of iron. I do not think this is the cause of low phosphate.

Let's look...

A typical dose of iron (my dose; see below) is, say, 2 ug/L. How much phosphate could that remove even if it ALL became ferric phosphate?

FePO4 is about 1/3 iron and 2/3 phosphate by weight.

So 2 ug/L of iron might combine with 4 ug/L of phosphate, or 0.004 ppm.

Typical foods daily add 0.02 to 0.3 ppm per day:
https://reefs.com/magazine/aquarium-chemistry-phosphate-and-math-yes-you-need-to-understand-both/
Thus, if you dose iron at my done once a week, you are only possibly precipitating 0.004 ppm out of a weekly food addition of 0.14 to 2.1 ppm of phosphate, or only 0.2% to 3% of the total phosphate.


This is from my Triton testing article:

Iron (Fe). The natural iron level varies a lot with depth, but surface seawater may have only 0.006 µg/L. The Triton LOD = 0.3 µg/L. I dose iron, and when I dose it I boost iron to roughly 1-2 µg/L, which would be detectable. This sample was taken more than a week after the last iron dosing, and none was detected as it gets depleted in the meanwhile. I’ve not yet seen a Triton test result for a real aquarium sample that had detectable iron, but that doesn’t mean these tanks are necessarily deficient. Iron is also a case where the form is critical, and ICP cannot distinguish form. Binding to organic matter, for example, can alter the bioavailability of iron.

Interesting. Thanks Randy. Maybe I will stop dosing iron. My reef was doing quite well without it.

 

[Randy Holmes-Farley Verified Community Expert]

Interesting. Thanks Randy. Maybe I will stop dosing iron. My reef was doing quite well without it.

It's certainly a fine thing to experiment with.

 

[anthonygf]

More likely, IMO, is the phosphate has spurred the growth of photosynthetic organisms such as micro algae, microalgae, corals, etc.

I have been increased my phyto dosing to almost daily. Still all animals are happy and growing.

 

[anthonygf]

I doubt it, unless you are intentionally dosing unusually large amounts of iron. I do not think this is the cause of low phosphate.

Let's look...

A typical dose of iron (my dose; see below) is, say, 2 ug/L. How much phosphate could that remove even if it ALL became ferric phosphate?

FePO4 is about 1/3 iron and 2/3 phosphate by weight.

So 2 ug/L of iron might combine with 4 ug/L of phosphate, or 0.004 ppm.

Typical foods daily add 0.02 to 0.3 ppm per day:
https://reefs.com/magazine/aquarium-chemistry-phosphate-and-math-yes-you-need-to-understand-both/
Thus, if you dose iron at my done once a week, you are only possibly precipitating 0.004 ppm out of a weekly food addition of 0.14 to 2.1 ppm of phosphate, or only 0.2% to 3% of the total phosphate.


This is from my Triton testing article:

Iron (Fe). The natural iron level varies a lot with depth, but surface seawater may have only 0.006 µg/L. The Triton LOD = 0.3 µg/L. I dose iron, and when I dose it I boost iron to roughly 1-2 µg/L, which would be detectable. This sample was taken more than a week after the last iron dosing, and none was detected as it gets depleted in the meanwhile. I’ve not yet seen a Triton test result for a real aquarium sample that had detectable iron, but that doesn’t mean these tanks are necessarily deficient. Iron is also a case where the form is critical, and ICP cannot distinguish form. Binding to organic matter, for example, can alter the bioavailability of iron.

From ICP test shows no iron.

 

[Randy Holmes-Farley Verified Community Expert]

From ICP test shows no iron.

That's normal, IMO. ICP tests cannot detect iron at natural surface seawater levels, at last last I checked with Triton.

 

[anthonygf]

That's normal, IMO. ICP tests cannot detect iron at natural surface seawater levels, at last last I checked with Triton.

I also have 2 iron test kits and they also show no trace of iron. I am not worried about.

 

[Randy Holmes-Farley Verified Community Expert]

I also have 2 iron test kits and they also show no trace of iron. I am not worried about.

Right, generally I do not think it is ever needed to be able to detect iron by kit. They cannot read low enough to read natural levels.

I suspect the only reason Red Sea suggests such a high iron level is so it can be detected with their kit. lol

Exact iron levels are not especially important. :)

 

[Dan_P]

Biom,

I had a similar question and I posted here: https://www.reef2reef.com/threads/iron-gluconate-vs-iron-citrate-and-other-iron-questions.234166/

I ran a test today. I dosed approximately .1ppm to our 50gal reef. Before dosing my phosphate was .1ppm and iron was undetectable. After dosing, iron was .1ppm and within 30 minutes the phosphate was at .06.

Definitely promising. My thread brought up the question about the differences with ferric iron and ferrous iron. It seems like ferric iron will precipitate slightly more phosphate than ferrous iron.

Then the final question would be, what ends up being more beneficial in our systems? The gluconic acid or the citric acid (assuming this is what citrate turns into).

Kent
Aqua Lab

A better test would be to remove a sample of water from the system and dose it, monitoring over time. The change you are seeing might be not be statistically significant. How accurate is your phosphate test kit?

An even better experiment would be to sterilize the water sample to remove all biotic processes.

 

[Dan_P]

I also have 2 iron test kits and they also show no trace of iron. I am not worried about.

Which iron tests? Some do not detect chelate iron. You can test your test by adding iron to a sample of your aquarium water and immediately testing it.

 

[anthonygf]

Which iron tests? Some do not detect chelate iron. You can test your test by adding iron to a sample of your aquarium water and immediately testing it.

I have the sera Fe and Seachem Multitest Iron kits. I will try what you suggest. Thanks.

 

[anthonygf]

Right, generally I do not think it is ever needed to be able to detect iron by kit. They cannot read low enough to read natural levels.

I suspect the only reason Red Sea suggests such a high iron level is so it can be detected with their kit. lol

Exact iron levels are not especially important. :)

Just another money making trick!?

 

[Laith]

I'm currently testing dosing Fe by adding 0.001ppm every four days. Been doing that for a couple of weeks now, mainly to see if it increases my chaeto growth (which is already quite rapid without the Fe addition).

From what Randy has been saying, this level of dosing should have a negligible effect on reduction of PO4 but still leave enough bioavailable Fe for the chaeto (and eventually the corals and other organisms).

 

[Cory]

I dose 5ml of Randys diy iron citrate to my 526 liter tank (like 150 gallons) daily. Its also what i believe Glenn f on here doses. I chose 5ml because its the max reccomended safe dose by glenn f. I haven't experienced anything bad from fish or corals. I have tangs too which are known to be sensitive to iron. In fact i think its beneficial to my corals. Every day i see new growth! Phosphate drops but little. For example ill read .54ppm dose 5ml iron citrate, tank gets a tiny fog, then check again and it dropped to .45ppm.
Edit i also use a 90 watt uv sterilizer which may change it.

 

[anthonygf]

I use BA Ferrion, on their label they say it is advisable to ensure that the concentration of phos not exceed 0.05 in the aquarium to be dosed. What do you make of that? My po4 was stable at around 0.08 and after dosing this po4 slowly dropped to 0.00ppm on Hanna po4 tester. Tested on Hanna ULR Phosphorous tester and got a reading of 21, next day 17, 13 and today 7. I did a 10 gallon water change with a sump cleaning and po4 is now 31 or 0.09ppm.

 

[Rich Klein]

I dose iron to feed my Chaeto, which reduces phosphate levels.....so yes.

 

[N.Sreefer]

Interesting, at work (farm) I use chelated iron and rock phosphate in grow media and I never noticed a detectable drop. I may be miscalculating the amount of phosphate different plants uptake if this is a continual process as the fertilizers break down. Thank you op for posting this.

 

[Laith]

I just ordered a pack of fergon tablets...

Randy, this is what I have found from you on how to use these:

"take 1 tablet and dissolve in 100 mL RO/DI (overnight soak). Let the solids settle out and use the liquid. Then I dose about 1-5 mL to my 200 gallons (dose is not critical) occasionally."

So how much Fe (in ppm) does this add (either per gallon or per your 200g)?

Thanks!

 

[Reefahholic]

It works, but depends on the system. It works better for those with more macro’s or algae in the system. It feeds the algae which results in more phosphate consumption from growth. Corals and microorganisms also consume Fe, which can have an effect on PO4 levels as they grow or multiply.

I’m dosing 10x the amount of Fe that I started with, and I see “zero reduction” in PO4 at this point in time, and everything is exactly the same. No changes.