Removing iron stains

[stev32k]

I have bad iron staining in the pool. It has been building up for the last two or three years and I could not find the source until recently. I believe it is coming from an iron ring around my underwater light. I checked the ring with a magnet and it is definitely iron. So I'll have that replaced and then acid clean the pool.

I confirmed the stains are iron by dropping three vitamin C tablets in a corner of the pool and the results were pretty dramatic. In less than an hour the area around the tablets went from a dirty yellow to a bright blue liner. It was pretty amazing. I spent a lot of time reading up on the Ascorbic Acid cleaning procedure here (thanks for posting it) and I believe I understand what needs to be done. I went to Jack's magic stuff site and read up on using the sequesterant and the part I don't like is having to test and add sequesterent on a routine basis after getting the stains off. I estimate the chemical cost (Jacks Magic Blue Stuff) to be close to $1,000 per year for my pool. That does not include the test kit ($93!) and testing supplies.

The only alternative to maintaining a sequesterent level to keep the iron in suspension, I can find, is replacing all the water in the pool. Is that right or have I overlooked something? I don't want to just pump the pool out all at once, although I've done that in the past when the liner was replaced and did not have any problem with ground water or with the sides of the pool caving in. My idea is to just put a water hose in the pool and let it overflow until the iron is below detection limits. I estimate it would take two or three weeks of running the hose 24/7.

The cost of the water will be about $300 - $600 at my rates and there will be increased costs for chlorine, CYA, and sodium bicarbonate. Those costs are worth it to me as the price of avoiding the aggravation of having to monitor another parameter for the pool. Does this sound like a reasonable thing to do and are there any alternatives?

 

[duraleigh]

Are you sure about your water costs? I did a totally anecdotal survey a year or so ago and found water rates to be about $5.00/1000 gal, if I remember correctly.

Yes, you must either sequester the iron or replace the pool water......unless you have a household water softener.

Having iron in a pool is a real PITA and you are being pretty smart to get rid of it.

 

[JasonLion]

While a light ring can release some iron into the pool, the quantities involved are usually so small that it wouldn't come anywhere close to staining levels. If it is releasing significant amounts of iron it should be very dramatically rusty with metal crumbling and flaking off over a significant area.

 

[stev32k]

My water rates are $2.68/1000 and the pool volume is about 32,000 - 35,000 gal. I'm guessing I'll need 5 - 8 turnovers to get the iron level down, but that is strictly a wag.

There was a black area on the liner around the light. At first I thought it might be black mold or algae, but after looking closer it was coming from the light ring. The ring has a thick coating of the black stuff that rubs off with your finger. I used a brush on the ring and it produced a serious cloud of what I am assuming is an iron compound.

If the iron is not coming from the ring I'm at a loss as to what could be causing the stains. The city water does not have any iron listed in the analysis they send out once a quarter and there is no other iron anywhere in the system that I can find. Everything is either PVC, vinyl, or 316 SS.

 

[stev32k]

unless you have a household water softener.

Hey, now that's an idea. I wonder if I could rent a softener(s) and rig up a temporary piping system to pump the pool water though?

Edit: Here is a picture of what happened when I dropped in the vitamin C tablets. The black spot is a leaf. The yellow staining in the picture is pretty uniform over the bottom and sides of the pool. The clear blue areas are where the tablets were.

 

[JasonLion]

If the staining only occurs right near the light ring then it is much more likely that the ring is the source and it is very unlikely that the iron levels in the bulk pool water are high enough to cause staining. In that situation you can most likely remove the stains with a localized ascorbic acid treatment and not need to use sequestrant or replace water.

 

[stev32k]

The staining covers just about the entire bottom and sides. It is not localized around the ring. Do you have any ideas where I might find iron in the system other than the light ring? I think you are right about ring not being the main cause. There is so much staining that I should be able to see deep pitting and flaking like you say, but there is none.

Could something besides iron be causing the stains and also be removed by Ascorbic Acid. As the picture shows the vitamin C tablets cleared up stains very quickly. Would they work like that on any other stain? I get a tremendous amount of oak leaves and acorns in the pool, but I would think chlorine would clear up those stains? Could there be iron in any of the pool chemicals other than HCL, or in the filter sand? I am really stumped.

 

[JasonLion]

The Vitamin C test you did plus the yellowish color of the stains both strongly point towards iron. There are other possibilities, but they are far less likely at this point.

Vitamin C would not have any effect on acorn/leaf stains. Organic stains from acorns and leaves respond to high FC levels.

There wouldn't be iron in any of the pool chemicals. The only common source is iron in the fill water, which becomes more concentrated in the pool over time. However it is possible to get iron from some trees/plants growing in high iron soil, but that is rare.

 

[DBfan187]

have you tried removing the light and seeing if it's the niche itself that's causing the issue?

 

[stev32k]

In thinking about it, the city water treatment plant is almost 50 miles from our house. Even though they don't report any iron in the system at the treatment plant the water could be picking up iron from the piping before it gets to us. Guess I need to test our drinking water at the tap. Can anyone recommend a good iron test kit?

 

[stev32k]

have you tried removing the light and seeing if it's the niche itself that's causing the issue?

I haven't removed the light in about 5 years. As I remember the fixture looked like either stainless or polished aluminum and there was no sign of rust or corrosion.

 

[POOLGOON]

Once the stain is lifted you could add a sequestrant to hold the metal in suspension, and do some research on a product call CUlator (see you later...get it). they claim to have the only product on the market to physically remove metal from the water, and it is relatively inexpensive depending on the concentration of metal in the water to begin with. I put one in my skimmer basket and left it there for about a month and compared it to the provided indicator. However I didn't have stains to begin with, and had a low concentration of iron in the pool (.5ppm) according to the lamotte iron/copper test kit. After the month I tested the water again for metal and the iron content was negligible ( about 0.1ppm, probabaly less). The CuLator pouch had a very light orange/brown tint to it, and i mean VERY light. My pH remains low enough to prevent any precipitation, but I would imagine once you do the AA treatment you'll be in the same situation I was....maybe not the the same degree though.

 

[stev32k]

I believe I want to try removing the iron using a water softener. They can be rented from a couple of different sources. The procedure I have in mind is this:

1. Modify the return piping from the filter to the pool with a tee and valves to send a side stream of water to a rented softener(s)
2. Bring the chlorine level down to zero and add Bauqual (sp?)
3. Lower the pH to 7.0 - 7.2
4. Treat the water with 1/2 - 1.0 lb of Ascorbic Acid per 1,000 gallons of water
5. Test the iron level and do not add sequesterant
6. Run the main pump 24/7 with part of the return water going to the softeners until the iron is removed

I don't think I can use chlorine while the softeners are in service because chlorine will damage the resin, but I'll have to confirm that with the softener supplier. That means I'll have to use the Baqual until the iron is removed. At a flow rate of 15 gpm though the softeners I estimate it will take about 2 weeks to remove the iron. Does that sound about right?

Will this work or have I overlooked something? Has anyone done this or something similar?

 

[duraleigh]

My first step would be an iron test. Followed by another iron test from a different source so you can clearly define your problem.

I didn't realize you could rent a water softener. The plumbing hookup and the salt consumption is going to be a LOAD of work.

 

[JasonLion]

Town water almost always has chlorine in it, and water softeners are routinely used with town water.

A greensand filter fed from a cover pump would be a simpler approach, though it could well end up being more expensive.

 

[stev32k]

I've ordered an iron test kit from Hach. It should be here next week. The rental softeners can be changed out with no regeneration required on site. They bring a regenerated unit in and just swap them out. I may just rent or buy a small pump and set it and the softener by the side of the pool and drop suction and discharge lines over the side.

The chlorine concentration in our potable water is quite a bit less (.2 - .4ppm) than the levels in the pool, but If I can use chlorine with the softener that would be great - one less chemical to buy.

I have a feeling that the iron in the city water must come and go. We've been in this house for fifteen years and only in the past two years has iron started showing up in the pool. This area has grown tremulously in just the past few years and the city has put in many miles of new water lines. So maybe if they quit messing with the pipe the iron will go away. I plan to start monitoring the iron concentrations when the kit gets here.

Since you guys have not told me it won't work I think I'll get started setting everything up. I don't have a price on renting the softeners yet, but they (Culligan) are supposed to get back to me Monday.

 

[DeadAquaRite]

I am dealing with this now (Picture here), and I strongly suspect my yard man is scattering fertilizer, then blowing the granules off the pool deck rather than avoiding the pool. If you use a lawn service, consider this as a possibility.