Brown Staining On Inner Walls of PVC Pipe

[Hanstb]

Could anyone please help me identify the cause of the straining on the interior walls of the pool piping shown in these pictures?

Our pool was drained to facilitate major maintenance and while removing some of the equipment in the pool shed, I noticed a thin, but stubborn, brownish stain on the interior of some of the pipes. The staining is only on the PVC pipe (Charlotte Pipe brand schedule 40 PVC) and appears to have only affected the suction side of the system before the filter, curiously enough the pump basket and strainer are not stained, and neither are the skimmers, floor drains or eyeball returns, the spa jets are also free of any staining.

Pool water chemistry before drawing was: (TF-100)
FC - 3.5
CC - 0.0
pH - 7.4
TA - 90
CH - 200
CYA - 40
Salt 3300

I have seen several references to iron producing brown stains on pool surfaces, our pool surface was completely free of any straining and the water contains no metals to speak of. These results are from our annual well water analysis, the tests are performed by a licensed laboratory and not a pool store, I also ran the iron test on the pool water itself using the Hanna HI-3834 test from the HACH Pool master kit and results where negative.

Aluminum 0.0
Arsenic 0.0
Barium 0.0327 (limit 0.70)
Cadmium 0.0
Coper 0.0182 (limit 2.00)
Chromium 0.0
Iron 0.0
Magnesium 0.0
Mercury 0.0001 (limit 0.001)
Lead 0.0
Sodium 114.5900 (limit 200)
Zinc 0.0136 (limit 5.00)

The plumbing (as well as the pump, filter, etc.) have been in continuous service for 7 years, while the pool chemistry may have been suboptimal at times in the past, there has never been iron or other metals in our water, and while calcium hardness and scaling has been an ongoing challenge, this does not seem to be related to hard water. The pool did have a Nature 2 system for the first three years, but I abandoned that gimmick 4 years ago, it was installed on the outlet of the filter beyond where the filter outlet picture was taken.

Unless this condition sounds any alarmas with more knowledgable members, I am inclined to ignore it as it does not seem to have caused any issues previously, and cleaning the pipes would be a huge chore, but I was surprised to see it!

Any ideas?

 

[duraleigh]

Probably iron deposits, but that is a guess. My pool had identical stains.....no harm, no foul. Inside skimmer was stained as well.

 

[Hanstb]

Thank you for your reply Dave,

How is it possible to have iron deposits without iron in the water? My skimmers (2) and my floor drains (2) are completely free of staining, it's only the pipe that is affected. I tend to agree with "no harm, no foul", but I am intrigued by what could be causing the staining.

 

[Hanstb]

Update...

I scrapped 'some' of the material from the pipe using a knife, the pipes have been dry for several days so the staining came off in powder form. I immersed the powder in deionized water and let it sit for a few minutes (terribly scientific, I know), then ran an iron test on the sample using the Hanna HI-3834 test kit, it reacted positive for iron!

I re-tested the well water and the small amount of pool water I have available for testing (the residual left over in the filter bottom), and both tested negative for iron, go figure.

All I can assume at this point is the iron level in the water is below the test kit's ability to detect (the lab also returned a 0.0 iron result) and the staining is the result of 7 years of gradual accumulation from trace amounts of iron, could that be the cause?

As for the selective nature of the staining, I am clueless, why is it on the suction side and not the discharge side of the system, the type of pipe used is the same, and why did it fail to adhere to the skimmers, drains, pump, filter housing, and the pool surface itself, it only took hold on the suction side PVC pipe. I find this all a little odd.

O' well, out of sigh and out of mind I guess...

 

[JamesW]

All water from natural sources has iron. It's probably just below the range that the test can do.

If you get a sample of water and boil off 90% of the water, that will increase the concentration 10x in the remaining water. That might give you a reading. Then multiply by 10.

Nature 2 contains copper and silver. The stains look like they contain silver. Did you put a Nature 2 cartridge in the pump basket?

If the Nature 2 was put in a skimmer or pump basket, the copper and silver would stain on the suction side. The filter would catch a lot of the metals, so you would not have as much on the filter output.

If you put tabs in the skimmer basket, that will oxidize the metals from there to the filter.

The stains probably contain iron, copper and silver.

Did you ever keep chlorine tabs in the skimmer?

How did you add chlorine when you had the Nature 2?

Do the filter cartridges get stained with a similar color?

 

[Hanstb]

No chlorine tabs have ever been used, the pool has always used a SWCG since new, including while using the Nature 2 cartridge.

Dichlor powder has been added on rare occasions to shock the pool and increase CYA, in those instances it was evenly distributed into the pool.

For the last several years, if and when the pool's chlorine demand exceeds the capabilities of the SWCG (or the cell has failed) we use liquid bleach to maintain FC levels.

 

[JamesW]

Where was the Nature 2 cartridge in the system?

Do you have staining at the cell output?

Is the cartridge in the filter stained?

 

[Hanstb]

The Nature 2 cartridge was installed between the filter and the cell, that line has no staining.

There is no staining after the SWCG cell.

The filter cartridges are old and very dirty (new cartridges are going in for the new fill), so I can't be sure if they have the same staining, it's just not visible.

I just found some staining on the back of the eyeballs for the return fittings, so it seems the source of stains was circulating throughout the pool and was just selective as to where it accumulated for one reason or another.

 

[JamesW]

I think that the stains look like silver. They probably contain some copper and iron as well.

 

[Hanstb]

Thank you James,

Should something be done to address the staining, or should I just let it be?

 

[JamesW]

Probably not much can be done now.

If you're doing a drain and refill, you're getting rid of the metals in the water.

Why are you doing a drain and refill?

 

[Hanstb]

We drained the pool to facilitate some construction work in the back yard that would have inevitably contaminated the pool, the stone decking is being sanded and re-polished so having it empty makes it easier to clean up when we're done. Emptying the pool also gave us the opportunity to address some minor tile issues that have arisen over the years and do some general maintenance.

There was nothing amiss with the pool itself, but the pool had not been emptied in 7 years so it's quite possible any contamination from the Nature 2 cartridges was still present in the water. The motive behind my research of late on this site has been to make the best of the opportunity that refilling the pool affords, and apply best practices going forward.

I just performed the test you suggested, after boiling off 90% of the water sample, the iron test still did not register, the min for this kit is 1ppm, so whatever iron is naturally occurring in the well water is minute.

Thank you!

 

[JamesW]

Your signature says softened well water. So, the iron should be low if all the water goes through the softener.

Did you have any staining of the plaster or is the plaster a dark color that would hide stains?

 

[Hanstb]

I took raw well samples to perform the iron tests, the lab results I posted earlier in this thread (iron 0.0) where also directly from the well. I have been using softened water to makeup for evaporation, but blend in raw well water to maintain the CH at 200, the well water CH is +/- 450. (My intent is to raise the CH to 350 on the advice of TFP.)

There are no stains on the pool's surface, but I do not have any plaster, the entire surface of the pool is glass tile and the grout is epoxy based.

Perhaps it would be beneficial to fill the pool with softened water and raise the CH in a way that does not introduce any raw well water, it would be more troublesome but certainly doable.

 

[duraleigh]

Here's something that I don't know but have suspected. Can tests for iron detect precipitate iron but not detect iron in soluble form? Would that influence your test results?

 

[Hanstb]

Dave,

That question is above my pay grade, the test I have on hand is the Hanna HI-3834 test kit, the literature on the Hanna website does not make that distinction, the kit's description is:

The HI-3834 Iron test kit determines the iron concentration in water by conversion of the ferrous (Fe2+) state. The test is fast, easy and safe. The colour cube makes it simple to obtain the iron level in water.

Iron can exist as ferrous (Fe2+) or ferric (Fe3+) ions. The HI-3834 test kit determines total iron levels in water via a Colorimetric method. First all ferric ions are reduced by sodium sulphite to ferrous ions. Phenanthroline complexes with ferrous ion to form an orange coloured solution, the colour intensity of the solution determines the iron concentration.

The lab test says: EPA Method 200.7 (ICP-AES), google brings up a 60 page document that is equally above my pay grade, but the result is 0.0, the report says the lowest detectable range is 0.00086 mg/L.

Bottom line, I am only concerned with health issues, if this is not going to harm my family and the pool looks great, then I'll leave it be, however, if there is a practicable way to avoid it, I would prefer not to see it persist or get worse.

 

[JamesW]

Iron can be in two forms, soluble ferrous iron (Fe⁺²) and insoluble ferric iron (Fe⁺³).

Some tests only measure ferrous iron. For a total iron test, a reducing agent, such as ascorbic acid or thiosulfate is added to convert the ferric iron into ferrous iron and then the test measures the ferrous iron.

I think that with fresh water and a new filter, everything should be good as long as no metals are added.

It seems that the iron level is pretty low.

I suspect that the worst of the stains are probably from silver.

With the Nature 2 gone, you should be in good shape.

 

[Hanstb]

James & Dave,

The literature for HI-3834 Iron test kit states that it tests for both ferrous (Fe2+) or ferric (Fe3+) ions and reports the total, which in my case is <0.1 ppm, so I should be good there.

Since there is no practical way to clean the piping, I'll just stick to the original plan, fresh water, new filters, and apply the TFPC protocol.

Thank you both for taking the time to share your thoughts, I sincerely appreciate it!

Best

 

[JamesW]

Cool. Thanks for being a gold supporter.

 

[duraleigh]

Thanks for being a supporter. Great looking dogs, by the way.