Dosing Iron to reduce Phosphates?

[biom]

Just wanted to start discussion here after passing thru GlennF's thread for DSR method where he suggest dosing Iron to reduce PO4 in tank water. http://dsrreefing.nl/phosphate.html
And I did fast and not really accurate test - put one drop of phosphate solution in two vials with tank water and in one of them put one drop of chelated iron solution, left them to rest for about 15 min and after that checked supernatant for phosphates with Salifert - and there were significant difference - almost no phosphates in vial treated with iron.
@Randy Holmes-Farley , @JimWelsh, @glennf any ideas how much will reduce how much, any constrains, experience etc. Thank you!

 

[rayn]

Interesting. Would like to know as well.

 

[Randy Holmes-Farley]

Yes, some people use iron for this purpose. I might use unchelated iron, but I can't be sure that is better.

It is easy to calculate the effect IF (and, unfortunately, only if) you know what forms from the iron. You may form some iron phosphate, but also will form iron hydroxide/oxide, using up alkalinity.

At best, 1 ppm or iron will bind 1.2 ppm of phosphate using ferrous iron or 1.7 ppm phosphate using ferric iron.

FWIW, the process is very similar to using lanthanum to bind phosphate.

 

[Aqua Lab Aquaria]

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

 

[Randy Holmes-Farley]

I think we need to keep perspective on how much needs to be dosed to see a substantial impact on phosphate.

IMO, you'd have to dose far more than I usually recommend, which is on the order of 0.003 ppm.

That is still far, far above NSW iron levels in surface seawater, but only capable of reducing 0.050 ppm phosphate to 0.046 ppm, even if every single iron ion precipitated with phosphate.

 

[Aqua Lab Aquaria]

Glenn states that his reef systems can tolerate up to .25ppm of iron.

I assumed that all iron test kits were testing free iron.

 

[Randy Holmes-Farley]

Wow, that's a ton of iron. I would not assume iron is only beneficial, but we'll just have to see what happens when more folks drive it so high.

I think that phenanthroline (a common way of detecting iron) can detect iron citrate. EDTA is more complicated, but it may not be able to detect it.

 

[Jon Warner]

Wow, that's a ton of iron. I would not assume iron is only beneficial, but we'll just have to see what happens when more folks drive it so high.

I think that phenanthroline (a common way of detecting iron) can detect iron citrate. EDTA is more complicated, but it may not be able to detect it.

Of course it depends on the form of Iron in the water... but producing NSW+ levels of Heavy Metals seems antithetical to everything we strive for in the hobby.

.25ppm of Iron in a Reef Aquarium?!?!?

 

[biom]

It is not only Glenn, Red Sea also recommend .15 ppm iron for fast growing systems. It will be interesting if somebody else share experience with long time exposure to high iron levels.

 

[Aqua Lab Aquaria]

So Randy, in light of these dosing volumes, is the glucose addition in Iron Gluconate appreciable for carbon dosing?

Have some more results from tests I've been running on our 50gal mixed reef. Pretty much just a skimmer and liverock/sand bio filter. I am using a Kessil 360WE which is supposed to have a UV component. How much, I don't know. Has SPS, clams, NPS, softies, anemones, sponges...

Tank was still getting one or two daily feedings for fish and coral (flakes, mysis, ROE, ReefRoids, Phyto, cyclopeeze). Not really holding back.

Here is a small video of the tank:


Starting at the begnning, before dosing, my chem was as follows:

Iron - 0ppm (Sera)
Phosphate - .1ppm (Hanna)
Nitrate - 5ppm (Red Sea)

I dosed 15mL of my FeEDTA13% solution and tested the following concentrations of iron at the following intervals post dose:

15min: .1ppm
30min: .1ppm
7hrs: .1ppm (Retested Phosphate at this time and it was .08ppm)
20hrs: a bit less than .1ppm but definitely detectable (Phosphate was .09ppm)
45hrs: 0ppm (Phosphate was .08)

My feeling is that the reduction in phosphate is attributable to more than just the error of the kits and is actually from the iron additions. 0.1ppm of FeEDTA13% seems to last about ~48hrs.

After taking the last Iron and phosphate reading at 45hrs post dose, I then proceeded to dose Iron Gluconate. I dosed 5.5mL to bring the tested concentration to .1ppm. Within 3 hours, I dosed 5mL more to bring the tested concentration to .25ppm. I also dosed two vials of biodigest in an attempt to reduce my potassium and help bring nutrients down. As Glenn has observed, my sailfin tang did show some minor stress/heavy breathing but is normal 24hrs later. My two clams showed no sign of stress. I also noticed some clouding of the water which disappeared within 24hrs.

24 hours after the final FeGluconate addition, my phosphate is testing at .07ppm. Iron is testing at 0ppm. In this test the FeGluconate dosing is confounding with the BioDigest dose, but it's interesting to note the further reduction of phosphate. From some previous reading, it appears that FeGluconate possibly favors bacterial utilization so there may be a two-fold action here of iron-phosphate precipitation and FeGluconate enhancement of heterotrophic bacteria.

Thoughts?

 

[Randy Holmes-Farley]

So Randy, in light of these dosing volumes, is the glucose addition in Iron Gluconate appreciable for carbon dosing?

The amount is smaller than I dose organic carbon by a considerable margin, but probably not insignificant.

When I dose vinegar, I dose about 100 mL per 200 gallons, or 5 grams acetic acid per 750 liters tank water = ~7 ppm every day

In ferrous gluconate, it is about 88% gluconate and 12% iron, so if you dose 0.2 ppm iron you are dosing 1.5 ppm gluconate.


FWIW, gluconate/gluconic acid and glucose are different molecules. Both are shown here:

http://www.novozymes.com/en/solutio...ghimprovement/Gluzyme-Mono/Pages/default.aspx

 

[Randy Holmes-Farley]

24 hours after the final FeGluconate addition, my phosphate is testing at .07ppm. Iron is testing at 0ppm. In this test the FeGluconate dosing is confounding with the BioDigest dose, but it's interesting to note the further reduction of phosphate. From some previous reading, it appears that FeGluconate possibly favors bacterial utilization so there may be a two-fold action here of iron-phosphate precipitation and FeGluconate enhancement of heterotrophic bacteria.

Thoughts?

I agree it may be hard to disentangle the effects, but thanks for posting it!

 

[jgalen0025]

Sorry to bring this up again but I have had a revelation with my reef keeping. I have been reefing for around 7 years and when I moved into my new home with a community well, I could not get sps to grow or color up (eventually died). Never had a problem before and everything was always automated. With that said I had to get a ten stage RO with 4 sediment filters to remove a large amount of iron. Every time I did phosphate a test on tank and supply water they were always undetectable even though i rarely did water changes (in response) and tried to increase them artificially. Seems Iron could definitely lower phosphate to the detriment of some people's tanks.

 

[jgalen0025]

Double Post, Please delete

 

[Randy Holmes-Farley]

Iron can only bring down phosphate to a degree similar to (or more likely, much less) than the amount of iron dosed on a molar basis. Most people who dose iron are dosing far, far less than the amount of phosphate in a typical aquarium.

So for people dosing amounts like my DIY recommends, the drop in phosphate from iron phosphate precipitation is trivially small.

 

[Laith]

Iron can only bring down phosphate to a degree similar to (or more likely, much less) than the amount of iron dosed on a molar basis. Most people who dose iron are dosing far, far less than the amount of phosphate in a typical aquarium.

So for people dosing amounts like my DIY recommends, the drop in phosphate from iron phosphate precipitation is trivially small.

I know that I'm reviving quite an old thread but if Fe binds with phosphates (therefore lowering phosphates) then the question is: Is there any Fe remaining in the water column to benefit what we would be dosing it for in the first place (eg chaeto in a fuge or for coral consumption)?

Or would the chaeto in this example take in the Fe bound with phosphates and be able to use both?

 

[Laith]

Sorry, never mind... I think I found some answers to this in the following post:

Iron dosing in presence of phosphate

I have a reef tank with 2-3 ppm nitrates and 0.2 ppm phosphate yet growth of algae on the glass is negligable even a week after scraping the glass. there are lots of collunista and stomaletta snails in the tank and they are probably doing some of the control, but even chaeto won't grow under...

www.reef2reef.com

 

[Cory]

I know that I'm reviving quite an old thread but if Fe binds with phosphates (therefore lowering phosphates) then the question is: Is there any Fe remaining in the water column to benefit what we would be dosing it for in the first place (eg chaeto in a fuge or for coral consumption)?

Or would the chaeto in this example take in the Fe bound with phosphates and be able to use both?

I think its available until it precipitates with phosphate. Its at that point that its no longer in the water dissolved but precipitated out of solution.

 

[Randy Holmes-Farley]

I know that I'm reviving quite an old thread but if Fe binds with phosphates (therefore lowering phosphates) then the question is: Is there any Fe remaining in the water column to benefit what we would be dosing it for in the first place (eg chaeto in a fuge or for coral consumption)?

Or would the chaeto in this example take in the Fe bound with phosphates and be able to use both?

There is precipitated iron phosphate which is not available, and there is always some iron remaining that is bioavailable.

 

[anthonygf]

Just wanted to start discussion here after passing thru GlennF's thread for DSR method where he suggest dosing Iron to reduce PO4 in tank water. http://dsrreefing.nl/phosphate.html
And I did fast and not really accurate test - put one drop of phosphate solution in two vials with tank water and in one of them put one drop of chelated iron solution, left them to rest for about 15 min and after that checked supernatant for phosphates with Salifert - and there were significant difference - almost no phosphates in vial treated with iron.
@Randy Holmes-Farley , @JimWelsh, @glennf any ideas how much will reduce how much, any constrains, experience etc. Thank you!

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.