Types of iron (well water)

[KLKelly]

I picked up a test kit (cheapo nutrafin one on sale) to test iron.  I was curious as I have well water that stains all the fixtures and the filter floss in my trickle tower for water change water is getting stained also. 

I was surprised because both test results came out zero!  So I've found out via google that there are different types of iron: "Red stains are normally caused by iron in the water. You must test to determine the amount and the type of iron you have. Some types are: oxidized, soluble, colloidal, bacteria or organic-bound".

The test kit measures Iron .0-1.0Mg/L.  "The test can also help distingish between chelated iron, which is more easily assimilated by plants and toxic non chelated iron".

Have I done the test wrong or is it possible that I have some other form of iron that the test doesn't recognize?

I am starting to use softened water.  I tested my main tank which is currently at 65% hard well water and 35% softened water.  Main tank has GH of 8, KH of 14 - no GH additives added yet.

Thanks guys.  Any good websites that discuss Iron in aquariums would be great also!

[BigDaddy]

Keyword = cheapo

Most iron kits get skewed results when using a test sample from an aquarium.  From my readings, dissolved organics, changing states of iron (ferric, ferrous, etc) and other factors can all mess with the end result.

I am assuming your samples are coming straight from the tap.  A well is much like an aquarium in the sense that dissolved organics, compressed gases and other factors are at play there too.

A good test kit will come with a reference solution that you can compare against to determine if your reagents are good.  I am pretty sure the nutrafin one doesn't.  Seachem's test kit does (I know because I owned one before I knew better).

[KLKelly]

Good information - Thanks!!!!

[kennyman]

I was under the impression that chelated iron was iron artificially bound with manufactured agents to prevent it binding to other elements? How is Iron not bound to a chelating agent toxic and what is it toxic to?

[BigDaddy]

Okay

Ferrous iron is soluble and ferric iron is non-soluble (I wrote that more to remind myself which is which).  One of the reactions of iron in water is the creation of free radicals.  Normally, antioxidants will manage these oxidizing agents.  However, in higher concentrations, the free radicals will oxide gill tissue, damaging or destroying it.

Chelators stop iron from reacting with the water (specifically the oxygen) until plants can process them.  The plants deal with the the chelators and gain access to the ferric iron which is preferred over ferrous iron.

[Glouglou]

This is parts of this statement find here:http://2the4.net/iron.htm

In groundwater systems iron occurs in one of two oxidation states: reduced soluble divalent ferrous iron (Fe+2) or oxidized insoluble trivalent ferric iron (Fe+3).

Ferric hydroxide (Fe(OH)3) is the direct result of ferrous iron oxidation and precipitation. With time, ferric hydroxide is mineralized.

amorphous hydrous ferric oxide (Fe2O3•XH2O),
maghemite ( gamma-Fe2O3),
lepidocrocite (gamma -FeOOH),
hematite ( alpha-Fe2O3), and
goethite ( alpha-FeOOH)
The above iron oxides are listed in order of decreasing solubility, which also reflects increasing crystallinity. Amorphous hydrous ferric oxide at neutral pH and oxidizing Eh conditions has a solubility of 0.6 µg/L, which is three orders of magnitude greater than that of goethite. However, high concentrations of iron in groundwater is not rare. Obviously, other processes are at work.

And this is, I believe some data on ferrous oxidation (without be combined to chelation agent or any ligand)

RON 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:

At pH 7.0, 90% Fe+2 oxidation requires 1 hour at 21o C and
10 hours at 5o C. At 21o C
At pH 8.0, 90% Fe+2 oxidation occurs in 30 seconds,
at pH 6.0 it requires 100 hours.
The critical dissolved oxygen concentration is 2 mg/L. Below that ferrous iron oxidation occurs slowly.
The above reactions are often responsible for the iron fouling of air strippers treating iron rich groundwater. These reactions can also foul screens in poorly designed recovery wells pumping that groundwater.

And now Iron complexing

IRON COMPLEXING

Ferrous iron is soluble as a cation, ferric iron is not. However, ferric iron can form soluble complexes with many inorganic and organic ligands, including compounds that are the byproducts of the biodegradation of aromatic petroleum hydrocarbons (catechols, which are organic acids resulting from aromatic ring cleavage). The yellow/orange coloration of groundwater at some sites contaminated with petroleum hydrocarbons is due to these ferric-catechol complexes.

It 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.

Humic acid, fulvic acid and tannic acid are examples on non-contaminant organic complexes. Phosphate also serves as a very effective complexing agent for iron.

We can see here that Ferrous and Ferric Iron can be complexed (chelated). Ferrous will stay in is ferrous soluble state longer and ferric will regain some solubility.

They will both be accessible to the plants, the only way they will be inaccessible it will be by mineralization or complete absence of complexing or chelating agents.

[fender316]

wow this is great Im gonna need to learn more, guess it didnt help that the SWAT team raided Glebe during 5 minutes prior to our chemistry exam, so we didnt have to do iT!  I probably would have failed it anyway, calculas was my strong point.  i'll probably will bring my water to that accutest lab to have them do a complete check-out, all these test kits end up laying around and hardly get used.  Learning a lot more here than i ever did in chemistry class, its one thing to be blasted with theoretical values that you have no interest in, until an actual application for it comes around.