I have removed all iron from my pool that was filled with borehole water

[Zeerob]

Hi,

I have a new pool and a borehole (and a new house too ). I wanted to fill my pool with borehole water, but found out that it contained a lot of iron. First, we used the borehole water for the house too, and you could taste the iron when showering. There was a lot of calcium in it too. I bought a calcium testset and an iron testset at a good aquarium shop. The iron was 0.2 mg / L, about half the scale of the test. The calcium was about 300 ppm, so acceptable for a concrete pool with tiles.
So, I filled the pool partly with the borehole water. I was wondering how to get rid of the iron. I have read of products that remove metals but these products are hard to buy in Portugal.
Then I added liquid chlorine. Within 30 minutes the water turned very brown. I turned on the pump, and could see that the filtered water was not brown. Because the pool was partly filled, the jets were above the water and could easily be catched in a bottle. After a night of filtering, the water was crystal clear. Then I re-measured the iron, and it was all gone! I have a Hayward cartridge filter and I cleaned it. It was full of brown powder (probably rust). I could wash most of it from the filter.
I have then filled the rest of the pool with borehole water and also with 25% company water. I repeated the same steps (add chlorine, filter, clean filter), and now the water is very clear.
I did not know that the chlorine would remove the iron for me, that was a real surprise .
Just to let you know.

Best regards,
Zeerob

 

[Zeerob]

Picture of the brown water after adding liquid Chlorine:



Let me know what you think !

 

[zea3]

It is possible to filter out iron that has precipitated out after chlorine has been added. If you have access to youtube you can look up homemade iron filters pool owners have set up to filter out the rust from iron filled water. It is an interesting process.

At this point you can choose to use sequestrant to prevent any iron filled water you may use to top off the pool from turning brown. Sequestrant breaks down over time and needs to be added regularly. If sequestrant is not available then you may choose to continue to filter the rust out of the water when needed.

 

[Zeerob]

Thanks for the info! I wonder why you would a separate iron filter when the main filter can do it as well. My cartridge filter is a bit brownish now, but that is not a big problem I think.
I will probably use tap water to top-up. Water price is progressive here (Portugal), the first 5 m3 per month are very cheap, price goes up and above 25 m3 it is very expensive (around 5 euro / m3). So, filling with tap water is expensive, but topping-up is not.

 

[Oly]

So 1 cubic meter (m3) is slightly more than 264 gallons and now 5 euro equals $6 US. So that is 2.3 cents US per gallon. If my calculations are correct that would be $534 to fill your pool. Now if all of your friends will bring over nice wine when they come to swim you can recover that cost in no time.

 

[Zeerob]

Ha ha, well it would still take longer as wine is really cheap here
But I have not received a water bill yet, so I am not completely sure how much it will be. There could be an extra charge for waste water.
And the borehole was very expansive, so I really want to use it.

 

[pabeader]

The reason for the separate filter is so that you can dispose of the filtered iron. Right now, with the iron trapped on your cartridge filter, it is slowly leaching back into the water. What really concerns me is that it might be doing so in a way that is much harder to get rid of.

 

[Zeerob]

I have cleaned the cartridges immediately afterwards. I could easily hose off the brown powder. Some spots did remain a bit brownish, but I think that at least 95 % was hosed off. If some would dissolve back in the water, I assume that it would react with the chlorine again, and be catched in the filter again. Why do you think it would be harder to get rid of?

 

[AftonJeeper]

Why do you think it would be harder to get rid of?

What you have been removing is oxidized iron, many here in the states have the same issue. What you don't see is the soluable iron that has not oxidized yet. It builds up over time and stains your pool, starts by turning white plastic a yellow color then begins to leave brown spots around the pool. Read up in pool school about metal stains for more info. You should also learn about using a sequesterant ( it keeps the metal in soluable form so it doesn't stain you pool). One of the recommended ones in Proteam Metal Magic.

Here is a recent thread about filtering out oxidized iron.
If you’ve got iron in your fill water, use Polyfill to remove it

 

[Zeerob]

Correct me if I'm wrong, but I think the iron was initially in solution. The water from our borehole is not brown. It turned brown when I added liquid chlorine. The resulting oxidized iron was filtered out.
I have measured iron with a test set before and after. Before it was 0.2 mg/L. After is was 0. So, I assume all iron is now gone.

 

[JoyfulNoise]

Correct me if I'm wrong, but I think the iron was initially in solution. The water from our borehole is not brown. It turned brown when I added liquid chlorine. The resulting oxidized iron was filtered out.
I have measured iron with a test set before and after. Before it was 0.2 mg/L. After is was 0. So, I assume all iron is now gone.

Is your tap water from a municipal supplier? Do they test and control for iron?

In the US, most municipal water suppliers neither test for nor remove iron as it is not considered a contaminant by the US EPA. Because of this, one can still get iron in their pool water even when using a municipal supplier. Also, many older water systems still use cast-iron delivery pipes (with very old lead welded joints) and so municipal water can have appreciable levels of iron in it from the distribution system.

If you start to see liner staining, then you are getting iron in your pool water. It will not always be filterable like is was on initial fill. More often than not, it will stain plastic parts and the liner itself. Using a sequestrant can help.

 

[Steve_in_C]

Probably the ground water from your borehole was low in oxygen as most groundwater is. The bacteria that oxidize dissolved iron and make it rust colored need oxygen. When you put the ground water in the pool you expose the water to oxygen. Theoretically the chlorine would kill the bacteria and stop this reaction. But if you did not add enough chlorine, add it quick enough, or let your chlorine levels go too low, the reaction could still occur. I assume that there is still dissolved iron that is below the resolution of your testing methodology. The iron that precipitated that you filtered out and removed from your filter is gone. You might try concentrating your water and retesting. You could do this by heating the water gently to cause it to evaporate to 1/2 its volume. The iron would not be removed by this method but would instead be concentrated. Then you could test and have a higher level of iron to test. You would have to divide your test results by 2 to get your iron level.

 

[Zeerob]

Is your tap water from a municipal supplier? Do they test and control for iron?

In the US, most municipal water suppliers neither test for nor remove iron as it is not considered a contaminant by the US EPA. Because of this, one can still get iron in their pool water even when using a municipal supplier. Also, many older water systems still use cast-iron delivery pipes (with very old lead welded joints) and so municipal water can have appreciable levels of iron in it from the distribution system.

If you start to see liner staining, then you are getting iron in your pool water. It will not always be filterable like is was on initial fill. More often than not, it will stain plastic parts and the liner itself. Using a sequestrant can help.

Sorry, I do not fully understand you reply. The water that I used to fill the pool was mostly from my own borehole. I only used 25% tap water. I do not have any data about the tap-water, but I have heard that it of good quality, and is generally used here to fill pools.

- - - Updated - - -

Probably the ground water from your borehole was low in oxygen as most groundwater is. The bacteria that oxidize dissolved iron and make it rust colored need oxygen. When you put the ground water in the pool you expose the water to oxygen. Theoretically the chlorine would kill the bacteria and stop this reaction. But if you did not add enough chlorine, add it quick enough, or let your chlorine levels go too low, the reaction could still occur. I assume that there is still dissolved iron that is below the resolution of your testing methodology. The iron that precipitated that you filtered out and removed from your filter is gone. You might try concentrating your water and retesting. You could do this by heating the water gently to cause it to evaporate to 1/2 its volume. The iron would not be removed by this method but would instead be concentrated. Then you could test and have a higher level of iron to test. You would have to divide your test results by 2 to get your iron level.

Sorry, this reply confuses me too. I assume the liquid chlorine that I added caused the oxidation of the iron to rust. I do not think bacteria have anything to do with it. The water turned brown only after (and immediately after) I added the chlorine.

 

[JoyfulNoise]

Sorry, I do not fully understand you reply. The water that I used to fill the pool was mostly from my own borehole. I only used 25% tap water. I do not have any data about the tap-water, but I have heard that it of good quality, and is generally used here to fill pools.

Where does the tap water come from?

 

[Zeerob]

The tap water is from the water company = the counsel here.

 

[JoyfulNoise]

The tap water is from the water company = the counsel here.

Are they required by law to report water quality? In the United States, all water suppliers must report water quality.

Unless they specifically treat the water to reduce iron in it, then that water can potentially be a source of iron. The bore hole water (we call it "well" water in the US) you use certainly has a lot of iron it.

If you use the tap water for topping off, that's better than the bore hole water.

 

[Zeerob]

I am not sure. I immigrated a few months ago and do not speak the language yet. The information is probably available somewhere. Many people have pools here, and the company / tap water is usually used to fill the pool as many do not have a borehole. I have heard that it is of good quality, and well suited for a pool. I ordered a borehole (143 m deep!) for my garden and for the pool. I did not realize that the borehole water might not be perfect for the pool. But, so far, I think it worked out well.
Yes, I intent to use tap water for topping up.