Copper Questions

[QPSUtah]

I recently acquired a pool maintenance and service business with one quite experienced service/repair tech and one new maintenance tech. So I’m still learning every day and trying to become the resident chem “expert” for the group.

Have a customer whose pH is unexpectedly dropping between visits (perhaps rain through smoked filled air?) and it seems, based on the blue color, that copper has gotten into the spa. (See pic).

Their CYA levels were also quite high so we went ahead and drained the spa and gave the plaster an acid wash, which I know has its detractors. It cleaned up the pool nicely. But several questions.

Does their equipment need to be flushed out? Or once the spa is filled back up and balanced, just start it circulating? Similarly, would you recommend replacing the filters? Or just start it up and try a sequestering agent for any remaining residual copper that may be in the lines?

Thanks in advance!

 

[JoyfulNoise]

If they’re floating pucks in the spa, many of them have copper added. That could be a source of copper and the cause of their low pH water as trichlor is acidic. Acidic water can also etch the copper out of the heater’s copper heat exchanger.

You should probably look at their chemical maintenance methods when your techs aren’t there.

 

[QPSUtah]

If they’re floating pucks in the spa, many of them have copper added. That could be a source of copper and the cause of their low pH water as trichlor is acidic. Acidic water can also etch the copper out of the heater’s copper heat exchanger.

You should probably look at their chemical maintenance methods when your techs aren’t there.

Thanks! Yeah, copper from the heat exchanger is a worry. I suspect it takes a long time to do real damage to it, so hopefully we aren’t there yet after just a couple weeks of seeing this.

 

[JoyfulNoise]

Thanks! Yeah, copper from the heat exchanger is a worry. I suspect it takes a long time to do real damage to it, so hopefully we aren’t there yet after just a couple weeks of seeing this.

Depends on how acidic the water gets. That’s the problem with trichlor in a small volume of hot water. It will exhaust the TA and then the pH will crash. You then have water that is highly oxidative from chlorine and corrosive from the low pH. Under extreme conditions, the heater can get damaged quickly.

I’d get rid of that floater and have them use liquid chlorine or figure out how to use an SWG in their setup. Trichlor is just not suitable for hot tubs.

 

[JamesW]

Can you show the plaster after the acid wash?

Can you show the cartridge filter?

How many tabs were used in how much time and how much water?

 

[QPSUtah]

Can you show the plaster after the acid wash?

Can you show the cartridge filter?

How many tabs were used in how much time and how much water?

I'm not sure how quickly they are running through tabs, but here is a picture of the plaster after the acid wash.

They were using trichlor tabs, so yeah, I think the TA just flipped and suddenly their pH was dropping each week. Makes sense. The plaster had a lot of purple/blue spots before, so it cleaned up nice.

 

[ajw22]

Review the chemicals being used and tell your customers NOT to use any chemicals that say "BLUE". Blue is a code word for copper in the chemicals.

Copper in Pool Water - Further Reading

www.troublefreepool.com

 

[JoyfulNoise]

Trichlor is just inappropriate to use in a hot tub/spa. It dissolves too quickly at high temperatures which can cause low TA, low pH and very high FC.

Either use the dichlor/bleach method or use bromine. Or use an SWG for chlorination. Trichlor is going to wreck the heater and people that pay other people to take care of their pools and hot tubs are simply too uninterested to care. And when the plaster and heater gets wrecked, they will blame you and expect you to fix it on your own dime.

 

[JamesW]

Their CYA levels were also quite high so we went ahead and drained the spa and gave the plaster an acid wash, which I know has its detractors.

What was the CYA level?

The copper heat exchanger will be damaged some for sure.

Exactly how much damage is difficult to determine without better data regarding the pH and FC levels and how long the chemistry was in the danger zone.

 

[QPSUtah]

What was the CYA level?

The copper heat exchanger will be damaged some for sure.

Exactly how much damage is difficult to determine without better data regarding the pH and FC levels and how long the chemistry was in the danger zone.

CYA was around 200 I believe. Free chlorine at our last check before draining was 1.5 and TA was 80 and ph was 6.5. I suspect it was off for a few days in total. But yes, hoping damage was minimal.

 

[QPSUtah]

Trichlor is just inappropriate to use in a hot tub/spa. It dissolves too quickly at high temperatures which can cause low TA, low pH and very high FC.

Either use the dichlor/bleach method or use bromine. Or use an SWG for chlorination. Trichlor is going to wreck the heater and people that pay other people to take care of their pools and hot tubs are simply too uninterested to care. And when the plaster and heater gets wrecked, they will blame you and expect you to fix it on your own dime.

I have them currently switched to dichlor for the moment. It is an inground spa so SWG is an option for them (they have one for their larger pool). I agree, Bromine might be a good option for them.

 

[JamesW]

CYA was around 200 I believe. Free chlorine at our last check before draining was 1.5 and TA was 80 and ph was 6.5.

1 lbs of trichlor in a 1,000 gallon pool will:

Raise fc by 110 ppm.

Raise CYA by 67 ppm.

Raise salt by 90 ppm.

Lower TA by 77 ppm.

You need 1.14 lb baking soda per lb of trichlor to offset the TA loss.

If the CYA was increased by 200, then the TA would have been lowered by about 230 ppm.

If the TA started at 80 and it got lowered by 230, it would be -150 unless baking soda was added on a regular basis.

If the TA gets to 0, then the pH is 4.5.

If the TA goes below 0, then the pH goes below 4.5.

At a TA of -150, the pH would be about 2.52.

pH = -log_10(0.00002X).

This modifies the formula a little bit to get the pH to 4.5 at a TA of 0.0.

pH = -log_10(0.00002X + 0.00003161)

TA...............pH
0..............4.5
-2............4.4
-3............4.2
-4............4.1
-5............4.0
-6............3.9
-7............3.85
-8............3.8
-9............3.74
-10..........3.7
-20..........3.4
-30..........3.2
-40..........3.1
-50..........3.0
-60..........2.9
-70..........2.85
-80..........2.80
-90..........2.74
-100........2.7
-200........2.4
-300........2.22
-400........2.1
-500........2.0
-5,000.....1.0.
-50,000....0.0
-500,000..-1.0

y = -log_10(0.00002 x + 0.0000316228) | y = 2.8 to 7 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

y = -log_10(0.00002 x + 0.00003161) | y = 4 to 7 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

pH vs. Negative TA.

 

[JoyfulNoise]

You might suggest to the homeowner that you’d like to perform a “heater check” where you remove the header and look for damage at the heat exchanger tubing. It would certainly cost money in parts (new sealing o-rings)and labor (a couple of hours of work) but at least you would assess the status of the heater. You took over care of that water body without a lot of knowledge about what had happened previously and without knowing the exact state of the equipment. You don’t want them blaming you for something that was not your doing.

 

[JamesW]

It looks like the customer has an automatic cover.

If that was kept closed, then there would be no chlorine loss due to UV, which increases the chlorine level over an uncovered pool.

Assuming a pH of maybe 2.5 and a FC of 20 ppm, or higher, the copper is definitely compromised.

What is the heater model number?

Some heaters have a sealed can that the heat exchanger sits in and some have a heat exchanger that is more accessible.

Not much you can do about the compromised copper other than watching for leaks.

 

[JamesW]

Different charts show different graphs, but they indicate that you can begin to get elemental chlorine gas at low pH which further increases the corrosion of the copper.

 

[JamesW]

-5,000.....1.0.

To lower the TA by 5,000 ppm in a 10,000 gallon pool, you would need to add 100 gallons of acid.

I'm pretty sure that the pH would not go down by 307.

It should only go down to about 1.


0.1 molar hydrochloric acid pH = 1.0.

1,000 gallons of acid will produce a pH of 0. (-50,000 TA).

10,000 gallons of acid will have a pH of -1. (-500,000 TA).

 

[JamesW]

Y = pH.
X = -TA

y=-log(0.00002x), y from 2.22 to 4.5 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

y = -log(0.00002x + 0.0000316228), x from 0 to 50 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

y = -log(0.00002x + 0.0000316228), y from 3.5 to 8 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

y = -log_10(0.00002 x + 0.0000316228) | y = 3.5 to 8 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

y = -log(0.00002x + 0.0000316228), x from -3 to 10 - Wolfram|Alpha

Wolfram|Alpha brings expert-level knowledge and capabilities to the broadest possible range of people—spanning all professions and education levels.

www.wolframalpha.com

 

[JoyfulNoise]

I think I can sum up all of @JanesW ‘s graph in one, easy to use, rule-of-thumb …

Trichlor bad, liquid chlorine good …

 

[SJPoe]

I think I can sum up all of @JanesW ‘s graph in one, easy to use, rule-of-thumb …

Trichlor bad, liquid chlorine good …

I'm often like...I understand all the individual words on the page...I just don't have a clue what I just read

 

[JamesW]

I have created a 9-Dimensional Graph that shows the relationship between the Amount of Trichlor used, Pool Size, Negative TA, FC, CYA, pH, Copper Corrosion, Heat Exchanger Life Left in Days and Temperature, but it only works with an 11-Dimensional Internet Website and Browser.