Iron and Chlorine mixing --- turns the Iron ferric (meaning, you can SEE it, and water color will change?)

jesser

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Hopefully this isn't too difficult a conversation but I really need to understand the process here and why...

I have high iron content in my well, but I also have 4 massive iron filtering tanks in the basement of the house to help keep things iron free. (yes these are even hooked in line with my outside water spigots (to prevent the bricks on the house from discoloring) and to help prevent iron from getting into the pool).

I'm trying to understand something however. I've read that if you have ferrous iron in your auto-fill-water, it might initially look clear, but as the auto-fill-water reacts with the chlorine in the pool, the iron will turn from ferrous to ferric which then turns your pool water a dirty green/brown. So....

Question #1 - Will iron turn from ferrous to ferric, and therefore discolor the water, -only- when FC is at SLAM level or higher? (I think the answer here is no?)
Question #2 - Will iron turn from ferrous to ferric, and therefore discolor the water, even if FC is below SLAM level? (I think the answer here is yes)
Question #3 - Is iron *MORE* likely to turn from ferrous to ferric when FC levels are generally higher than lower (for example, FC of 8 versus FC of 3.5)? (I'm not sure of this answer at all)

The reason I'm asking those 3 questions is, I'm finding right now that when my auto-fills are running (especially in my lower pit, which is a separate 1600 gallon water basin for my pool's disappearing edge), that the water quickly turns from clear to a greenish/brown (caveat --- I'm colorblind, but it's not def algae). And I'm wondering if lowering my FC levels overall (I admit I keep my FC on the high side, typically 8-10, w/CYA around 50) would help keep iron in it's ferrous (invisible) state and therefore -not- change the color of the water, or at least not change it so quickly.

If anyone can help with answer those 3 questions to start, that would be great. I will have more follow up questions for sure, but this will help get the ball rolling.
 

JoyfulNoise

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Ferrous iron (Fe2+) is not stable under normal water conditions and will react with both chlorine and dissolved oxygen. Ferrous iron will always turn into ferric iron, it's just a matter of when and where it happens. Even with chlorine present, ferrous iron will eventually oxidize to ferric iron. The concentration of chlorine in the water simply drives the overall rate of the reaction, the more FC, the faster it is likely to go. pH has a big impact on iron stability but you really can't keep your pH low enough without damaging your pool.

It sounds like you have very high iron levels from your well. There is also the possibility of manganese contamination in high iron wells. Manganese tend to turn water black. I'm assuming at some point you had the raw well water analyzed and the filters were sized appropriately to handle that. If you're still getting iron at the fill point, then you need to look at shaving those filters serviced or replaced.
 

jesser

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Appreciate the response. What I don't understand is... if I test the level of iron in my water using a tester I bought (reagent test), I get .56ppm -before- my filters, and 0.00pm -after- my filters (i have (4) very large 13x54 tanks). but even at 0.00ppm, my pool water still discolors when the auto-fill is putting in substantial amounts into into my pool --- I just don't understand that. We don't have copper in our wells (so I'm told) in this area at all. Am I better off taking a water sample to my local county to see what result they come up with for a water analysis? (I'm assuming they will do that?) It just doesn't make sense to me that my iron tests are showing 0.00ppm with the auto-fill water but my water is still turning color. Eventually the water in my pool clears up, as my DE filter (filled with Fiber Clear) does seem to eventually clear up the water.
 

jesser

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I'm just gonna add... I've been thinking about this, and I'm really struggling still to understand the answers to my 3 questions above.

and, @JoyfulNoise ---- when you said, "Even with chlorine present, ferrous iron will eventually oxidize to ferric iron" Did you mean to say, "Even -without- chlorine present..." ?? Would you say that i likely DON'T have iron in my water if I'm testing the water right from the auto-fills and finding that water is reading 0.00ppm of iron (using Milwaukee MW14 iron tester with a MI528-0 reagent.
 

JoyfulNoise

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I'm just gonna add... I've been thinking about this, and I'm really struggling still to understand the answers to my 3 questions above.

and, @JoyfulNoise ---- when you said, "Even with chlorine present, ferrous iron will eventually oxidize to ferric iron" Did you mean to say, "Even -without- chlorine present..." ?? Would you say that i likely DON'T have iron in my water if I'm testing the water right from the auto-fills and finding that water is reading 0.00ppm of iron (using Milwaukee MW14 iron tester with a MI528-0 reagent.

Correct, “even without” is what I meant. Any dissolved iron (Fe2+) in pool water at typical pool pH will not be stable but will want to covert to iron oxide (Fe3+). Chlorine just helps the process go faster.

I would agree that your filtration system should be able to keep iron out of your pool. Your testing seems to indicate it’s working as designed. So the question is, are there any other sources of iron you can think of? Water runoff into the pool? Fertilizer?

How much staining are you seeing?

Have you measured the iron levels in your pool water (you need to let the chlorine drop to zero)?
 

jesser

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I haven't tested the pool water itself for Iron. @JoyfulNoise Why do I need to let FC drop to 0 to test for Iron?

I'm not getting any staining at all.... Long story short, my main pool (32,000 gallons) has an auto-fill on it, and my lower pit (1,600 gallons) has a separate auto-fill on it. If the lower pit gets low (this is the water runoff from the main pool's disappearing edge), then the lower pit will have water added by its' own auto-fill (or by me adding water to the lower pit via a hose from an outdoor spigot). When water is added (by either of those 2 methods, or both methods), the water is more greenish/brown (I think --- I'm colorblind) than my crystal clear pool water. The water in the lower pit is sucked out regularly and recycled back -into- the pool which then introduces that discolored water into the pool. Eventually, any of that discolored water (again, I think it's a greenish/brown, but... ugh, colorblind) gets cleaned up by my Jandy DE-60 filter (using Fiber Clear). I'm basically just trying to find out, WHY when my lower pit gets discolored when large amounts of water are added to it from the auto-fill (or hose/spigot). It might NOT be Iron. But we do have HIGH Iron content in our wells here. Yet my reagent testing shows 0.00pm Iron when I test the auto-fill and the hose-spigot water (and .56ppm -before- my Iron filters).
 

jesser

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Some pics. The pit it just plaster over gunite. There's nothing else in it. 2 drains that suck water out of the pit and send it back into the pool or up to the slide.

1627314439633.png

1627314363757.png
 

JoyfulNoise

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To answer the previous question, chlorine can interfere with the phenantroline method -

Interference: Among the interfering substances are strong oxidizing agents, cyanide, nitrite, and phosphates (polyphosphates more so than orthophosphate), chromium, zinc in concentrations exceeding 10 times that of iron, cobalt and copper in excess of 5 mg/L, and nickel in excess of 2 mg/L. Bismuth, cadmium, mercury, molybdate, and silver precipitate phenantroline. The initial boiling with acid converts polyphosphates to orthophosphate and removes cyanide and nitrite that otherwise would interfere. Adding excess hydroxylamine eliminates errors caused by excessive concentrations of strong oxidizing reagents. In the presence of interfering metal ions, use a larger excess of phenanthroline to replace that complexed by the interfering metals.

So you should let the sample sit until the FC goes to zero or perhaps try to use some R-0007 thiosulfate to reduce the chlorine. Either way, you might want to test the water in the well to confirm if iron is present. Unfortunately, iron testing is not as simple as using a photometer because if the iron precipitates, you won't be able to measure it. There's an entire extraction and digestion process using boiling acids to ensure all the iron is properly accounted for. Outside of a chemistry lab, that's hard to do.
 

jesser

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So, to clarify.... when I am using my Milwaukee MW14 iron tester, and I get .56ppm (before my iron filters), and get 0.00ppm after my iron filters, you are saying that the 0.00ppm isn't necessarily accurate and that I'm still possibly adding iron into my pool via my auto-fills, despite what the meter reads?
 

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JoyfulNoise

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So, to clarify.... when I am using my Milwaukee MW14 iron tester, and I get .56ppm (before my iron filters), and get 0.00ppm after my iron filters, you are saying that the 0.00ppm isn't necessarily accurate and that I'm still possibly adding iron into my pool via my auto-fills, despite what the meter reads?

I want to say that a zero reading is meaningful but, with iron testing it isn’t always true. You could have had some dissolved iron in the sample water but it converted very quickly to insoluble iron and the test will not detect that. If you actually read the EPA test protocols for phenantroline method of iron detection, it requires a lot of sample processing to get an accurate evaluation. All that is to say, if you had a gross iron contamination, your tester would see that. With minimal concentrations, your detector could easily be fooled.

Another possible source of iron are those large stones in the basin wall. Natural rocks and stones contain significant amounts of iron. It is possible for pool water to leach iron from stones especially if those stones are ever cleaned with an acidic descaling solution.
 

jesser

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I decided to contact a private testing laboratory nearby that analyzes well water and drinking water, for anything you want tests done on. Going to take some samples to them for the water, before and after, my four 13x54 filters to see how much Iron and/or other junk is in the water. There standard test is for 3 metals, (iron, lead, and copper). But i can choose the metals I want... what would you recommend?

I'm not sure my Milwaukee MW14 tester is really measuring accurately. I'll get them test samples tomorrow, should hear back in 7-10 days they say.
 
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JoyfulNoise

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Iron
Copper
Manganese

In wells that have high iron levels, manganese can also be present. It only takes a small amount of manganese to make water turn a dark brown or black color.
 

revitup

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I decided to contact a private testing laboratory nearby that analyzes well water and drinking water, for anything you want tests done on. Going to take some samples to them for the water, before and after, my four 13x54 filters to see how much Iron and/or other junk is in the water. There standard test is for 3 metals, (iron, lead, and copper). But i can choose the metals I want... what would you recommend?

I'm not sure my Milwaukee MW14 tester is really measuring accurately. I'll get them test samples tomorrow, should hear back in 7-10 days they say.
Watching this to see the iron level the lab comes up with vs the MW14 tester.
 

jesser

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Thanks @JoyfulNoise ... I stopped off at the testing location to pick up 3 sample containers. I'm going to fill each of the 3 with:

1) Straight well water (before my (4) iron filters treat any water)
2) Water after my iron filters
3) Water after my iron filters (when the filters have had more than 2000 gallons run through them since the last backwash/regeneration cycle)

I think I will test for
a) Iron
b) Copper
c) Manganese
d) Magnesium

Testing is 7-10 days.
 
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