Question on Copper Staining - Actual quantity of copper in a stained pool

[del]

I have been experimenting with my pool, probably more than I should. Recently, I let the PH go below 7, which was a big mistake. I mobilized a lot of previously plated copper on my pebbletec. Bringing the pH above 87 caused much of the copper to replate on the pebbletec. I am not using a sequestrant, and probably do not want to start. In doingk all of this, some of the copper or compouds of copeper stayed in solution. My water sent green with the addition of liquid chlorine. By adding ascoric acid, I got it to turn a beautiful blue - very beautiful actually. And, it was very sparkling clear. No algae is present on the walls at this time.

My pool is 14 years old and I had previously used copper algecides, so I am not surprised that I have lots of uniform copper staining. I read lots of posts, and I think I know what is going onj pretty well and I think that I know what to do to at least temporarily deal with it with sequestrants. Anyway, I am posting in the deep end to get some insight into this issue for purposes of discussion and understanding. I downloaded a really good solubility graph for the solubility of copper in water. vs. pH At about pH of 7, up to about 1 PPM or so of copper can be dissolved in the pool water. At about pH 8, very, very little can be dissolved. Being in San Diego and being with a SWG the pH almost always climbs up and I think that the dissolved copper will drop our of solution and again just get "plated" onto the pebbletec.

I started to use the large size Culator to see if it would take the dissolved copper out. I think that it did take it out, even at pH of about 7.2, based on the LaMotte copper test kit I purchased. I still have lots of "plated" copper on the pebbletec. If I keep adding acid (ascoribic acid), I can again get the copper to dissolve and I think that the Culator can then remove it again. The pH will no doubt go up, and I will have to constantly repeat this cycle. I do not now how may times I need to do this, or how may Culators I may need to purcahse to remove the vast majority of all of the copper. So, I am curious if anyone has any idea of just how may ounces/grams/pounds of copper may actually be adsorbed onto a pebbletec surface. When I recently drained my spa, I could see uniform staining on the pebbletec, so I am guessing that there may be a lot, but I am not really sure. Again, I know that I can add sequestrant to hide the problem, but am curious just how much copper I may be looking at removing if I stay with my plan to remove it with Culators. I could just add a lot of ascorbic acid and then drain the pool, but San Diego water is expensive as I have stated in some of my prior posts, and I, or course, like to tinker so that draining the pool would not satisfy my curiosity. Also, I checked the copper content from my kitchen tap, and it was about 0.4 ppm or so based on the LaMotte test, so I may not actually fix the issue with a drain and refill. Hopefully, I have not confused everyone with this one. Any comments would be appreciated. Thanks,

Del

26,500 gallon pool/swim spa (Spa part is 3300 gallons)
pebbletec finish
14 years old
SWG
DE Quad Four Filter
Waterfall waterfeature
Vanishing Edge with pump
Submerged Surge tank for vanishing edge
Currently Zero ppm copper and iron in the water
Visible copper stains
Confirmed copper in water prior to Culator
about 140 CYA
About 600 CH
Zero free or combined chlorine with DPD test
Pentair Intelliflo (1) for main filtration
Whisperflos (3) for various waterfeatures

 

[kimkats]

Interesting idea and thoughts. I think you are on the right track with what you are doing but have nothing to base that on except my gut. This should bump it up so others can see it.

 

[duraleigh]

As long as you use your tap water as refill, I think your problem will continue. .3 PPM is a number generally used as a threshold for copper problems and you are above that.

Copper in tap water is very unusual. Do you have anything in your house that could be the source? Copper pipes, etc.

 

[JoyfulNoise]

Those testers for copper are not usually accurate at low levels. Most only go down to 0.2-0.4ppm and, at that point, it's statistically the same as zero. You very likely do not have copper in your tap water. I would imagine that living in San Diego means you are on city water and, if so, copper in the water would be a big red flag for the water utility.

Ascorbic acid is not very good at removing copper. In fact, it can make copper staining worse. You more than likely have copper and iron staining and the ascorbic acid is doing all of it's "magic" on the iron. The only real solution to your problem is to use Jack's Magic Stain removal protocol for copper and then dump all of the pool water. The Jack's Magic regimen uses a series of chemicals to remove and sequester the copper BUT you really need to dump the water after that to ensure the copper is gone for good. In a pool your size, you're probably looking at a couple of hundred dollars in chemicals and then whatever it costs to replace the water (and any fines or levies for high water volume use).

Do you have a heater? If so, it will have to be bypassed or taken out of service while you remove the copper because the Jack's Magic Protocol will also strip copper out of a heat exchanger.

 

[del]

A recent San Diego water quality report shows essentially no copper in the water, and I believe them. My kitchen RO water shows zero copper, which is to be expected. My kitchen taps shows copper using the LaMotte test. Yes, I have copper piping in the house and it may be a source of copper, but I really do not know the source for sure. The LaMotte test kit test is fairly inexpensive and registers values between zero and 1 ppm. I have confidence in that test, as I used a crudly made copper solution made with a copper sulfate and water from my RO water and I got the expected value when tested. I did a kitchen table test and now think that the Jack's Purple does mask the copper from the LaMotte test, which is no surprise, as the copper is not longer free. Taylor has a very expensive free and total copper test kit, but it is over my budget, so I guess that I will have to keep guessing the total copper content. I do not own an iron test kit, but maybe I should get one.

I sort of agree on the ascorbic acid comments, thank you. I have now tried citric acid, which temporarily turned the water very clear. Now the water is back to a pale blue, but a good looking blue. If I want to just solve the problem without learning more, I agree that I should acidify the pool, let it sit awhile and then drain it and start over. Water, even at over once cent per gallon here may be less expensive than using all of the chemicals that would also not necessarily be successful. If I decide to do this, what acid should I use? I think the choice is between citric and maybe muriatic. Nobody suggests muriatic - is there a reason that it should not be used if the water if never pumped throught the pool equipment and there is no exposed metal in the pool?

I may still experiment a bit before dumping the water, just to learn a bit more. It is an interesting situation. If I learn something, interesting, I will pass it along. I am still curious about my original question in terms of how much copper may actually be on the pool walls. I attached a picture in case it helps. I placed a white plate on the bottom of the spa so that the color of the water can be seen, in an attempt to distinguish its color from that of the pebbletec finish.

Thanks for all of the comments.

Thanks for the comments.

 

[JoyfulNoise]

The Jack’s Magic system uses sulfamic acid to remove the copper and a sequestering agent to hold it in solution. If you just want to remove the copper and dump the water, then they can just sell you the sulfamic acid without the sequestrant. You don’t want to use muriatic acid as that can easily damage plaster surfaces, tile grout and equipment.