Sulfate Build up in Exchanger

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ETichansky

In The Industry
Jan 24, 2024
3
Valencia, PA
For the past year, sediment has built up in the heat exchanger, it needs to be cleaned out before the heater will restart. The company we work with had the solid "blue chips" analyzed and it was determined that the makeup was: SULFATE 1070 Mg/kg, Nickel 987 ppm, Copper 8159 ppm, and Chloride 1124 ppm. The pool water was also analyzed and the contents were: SULFATE 16 mg/L, Nickel <0.01 mg/L, Copper <0.01 mg/L, and Chloride 847 mg/L.

The source water has been changed from well to public, Pool Metal Magnet has been added regularly for years due to the metals in the well water. The heat exchanger was changed from a copper/nickel blend to a pure copper part and the result has produced very little if any change. Recently when the heat exchanger was cleaned the substance was a clay-like substance versus the chip substance that was previously found.

The heater was replaced about a year ago and is a Raypak. The heat exchanger on the old heater, also a Raypak, was cut open and the same substance was found in it. The old heater did not have the fail-safe that would not allow the heater to be turned back on unless the exchanger had been cleaned out. This is an indoor pool and it is open year-round. The clogs happen anywhere from one week to three weeks after cleaning.

Ideas, thoughts, solutions?

I appreciate your help,
Emily
 
ETichansky said:
SULFATE 1070 Mg/kg, Nickel 987 ppm, Copper 8159 ppm, and Chloride 1124 ppm.
Click to expand...
Sulfate = 1 part per thousand or about 0.10%
Nickel = = 1 part per thousand or about 0.10%
Copper = = 8 parts per thousand or about 0.80%
Chloride = = 1 part per thousand or about 0.10%

That's only about 1.1% of the composition.

What is the other 98.9%?
 
Welcome to TFP.

This a public commercial pool or private residential pool?

What is the water chemistry and how is it maintained with what chemicals and frequency?
 
ETichansky said:
Pool Metal Magnet has been added regularly for years due to the metals in the well water.
Click to expand...
That will break down into phosphates and it might be the main cause of the scale.

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Calcium phosphate scale

Can you explain Calcium Phosphate Scale and how do you remove it
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Are you watching CSI (The water chemistry parameter, not the TV show).

If yes, what is the highest that it has ever been?

What are all of the chemistry readings including phosphates, calcium, water temperature, CSI, TA, Ph, Salinity etc?

Are you using chemistry automation with pH and ORP?

If yes, what are the set points?

How much acid are you using weekly?

Are you using hydrochloric acid, sulfuric acid or carbon dioxide to lower the pH?

Are you using any type of "Buffered" or low-fuming acid?

What is the chlorine source?

Can you test and report the salinity using a K-1766 salt test kit and a good salt meter set to salinity?
 
Hi James, thanks for your response. My answers to your questions are below in red. I have attached an analysis of the pool water and the sediment found that was completed by a lab in July.

Our source water was a well and we have had issues with metals turning the water green that have been controlled by Pool Magnet Plus which you mentioned could be an issue. Since changing our water to public to fill we have had issues with film and bubbles in which we add Calcium Chloride to combat.

I appreciate your time, thoughts, and what you suggest as a solution.


Are you watching CSI (The water chemistry parameter, not the TV show). No

If yes, what is the highest that it has ever been?

What are all of the chemistry readings including phosphates, calcium, water temperature, CSI, TA, Ph, Salinity etc?
Phosphates - I do not have a kit for this - I can look into it
Water Temp - 87 - 89
CH - 550
CSI - 0.14 according to the online calculator from Pentair
TA - 70 - we need to add sodium Bicarbonate every other week or so
pH - 7.3
Salinity - I do not have a kit for this - I can look into it - this is not a Salt water pool

Are you using chemistry automation with pH and ORP? Yes

If yes, what are the set points? pH - 7.5; ORP 720 (we purposefully try to keep the Chlorine level around 2.0, we have struggled to find the correct set-point for this and have to adjust the set-point every couple of weeks)

How much acid are you using weekly? It is pumped out of a 15-gallon jug that is changed approximately every 3 -4 weeks

Are you using hydrochloric acid, sulfuric acid or carbon dioxide to lower the pH? Hydrochloric Acid

Are you using any type of "Buffered" or low-fuming acid? NO

What is the chlorine source? Calcium Hypochlorite mixed with water

Can you test and report the salinity using a K-1766 salt test kit and a good salt meter set to salinity? I will have to get one, but yes.
 

Attachments

  • 2023, 07-24 Lab Sample results.pdf
    110.2 KB · Views: 3
ETichansky said:
Calcium Hypochlorite mixed with water
Click to expand...
You might want to switch to sodium hypochlorite or maybe SWG (Salt Water Generator).
ETichansky said:
Phosphates - I do not have a kit for this - I can look into it
Click to expand...
The phosphates are likely to be an issue.
ETichansky said:
CH - 550
Click to expand...
That is getting into the high range.
ETichansky said:
CSI - 0.14 according to the online calculator from Pentair.
Click to expand...
Is the CYA 0?

You need the CYA and the salinity readings to get an accurate CSI.

The temperature in the heater is higher than the pool water and this increases the CSI as you can see on the calculator.

Once you go above 0.0 for the CSI, the risk of scaling goes way up.


1706135251105.png1706135293357.png

You should track the CSI carefully and keep it in the -0.3 to 0.0 range.

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ETichansky said:
TA - 70 - we need to add sodium Bicarbonate every other week or so
Click to expand...

ETichansky said:
pH - 7.3
Click to expand...
If you target a higher pH, you can use a lower TA to reduce pH rise from carbon dioxide.

HCO3- + H+ --> H2CO3 --> H2O + CO2

The bicarbonate converts into carbon dioxide like this and the pH rises because you are removing free hydrogen ions.

The carbon dioxide offgasses and is lost.

The amount of carbon dioxide created determines the rate of pH rise.

The amount of carbon dioxide depends on the pH and the TA.

There is always a specific percentage of the TA that turns into carbon dioxide.

pH....................%CO2
7.0........................18.292
7.1........................15.097
7.2........................12.377
7.3........................10.088
7.4........................8.183
7.5........................6.611
7.6........................5.324
7.7........................4.275
7.8........................3.426
7.9........................2.741
8.0........................2.189
8.1........................1.747
8.2........................1.392
8.3........................1.109

Targeting a pH of reduces the Carbon Dioxide by a factor of about 1.93 times, which means that the pH rise is reduced by 1.93 times.

If you also drop the TA to 50, the the pH rise is reduced by about 2.7 times.

You can use the formulas to calculate the percentage of bicarbonate vs. carbon dioxide or carbon dioxide vs. bicarbonate.

100÷(1+10^(6.35 – 8.3)) = 98.890% bicarbonate vs. carbon dioxide.

100-(100÷(1+10^(6.35 – 8.3))) = 1.109% carbon dioxide vs. bicarbonate.

1706135573154.png

plot y = 100÷(1+10^(6.35 – x)) and y = 100-(100÷(1+10^(6.35 – x))), x from 4 to 9 - 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 www.wolframalpha.com
 
I suspect that the scale is probably mostly calcium carbonate and calcium phosphate.

Check the phosphates and maybe do a treatment if they are really high.

I would get a filter for the fill water that removes metals so that you do not need metal sequestrants.

I would try to keep the pH higher, the TA lower and the CH lower as well.
 

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ETichansky said:
Hi James, thanks for your response. My answers to your questions are below in red. I have attached an analysis of the pool water and the sediment found that was completed by a lab in July.

Our source water was a well and we have had issues with metals turning the water green that have been controlled by Pool Magnet Plus which you mentioned could be an issue. Since changing our water to public to fill we have had issues with film and bubbles in which we add Calcium Chloride to combat.

I appreciate your time, thoughts, and what you suggest as a solution.


Are you watching CSI (The water chemistry parameter, not the TV show). No

If yes, what is the highest that it has ever been?

What are all of the chemistry readings including phosphates, calcium, water temperature, CSI, TA, Ph, Salinity etc?
Phosphates - I do not have a kit for this - I can look into it
Water Temp - 87 - 89
CH - 550
CSI - 0.14 according to the online calculator from Pentair
TA - 70 - we need to add sodium Bicarbonate every other week or so
pH - 7.3
Salinity - I do not have a kit for this - I can look into it - this is not a Salt water pool

Are you using chemistry automation with pH and ORP? Yes

If yes, what are the set points? pH - 7.5; ORP 720 (we purposefully try to keep the Chlorine level around 2.0, we have struggled to find the correct set-point for this and have to adjust the set-point every couple of weeks)

How much acid are you using weekly? It is pumped out of a 15-gallon jug that is changed approximately every 3 -4 weeks

Are you using hydrochloric acid, sulfuric acid or carbon dioxide to lower the pH? Hydrochloric Acid

Are you using any type of "Buffered" or low-fuming acid? NO

What is the chlorine source? Calcium Hypochlorite mixed with water

Can you test and report the salinity using a K-1766 salt test kit and a good salt meter set to salinity? I will have to get one, but yes.
Click to expand...
15 gallons of acid each month? That’s a lot of acid. It would be hard to believe this was not related to the issue. I used just about 2 gallons over a 4 month period in a 27k gallon pool since mine was replastered. It doesn’t say what size the pool is but maybe it’s very large?
 
ETichansky said:
TA - 70 - we need to add sodium Bicarbonate every other week or so
Click to expand...

Bperry said:
15 gallons of acid each month? That’s a lot of acid. It would be hard to believe this was not related to the issue.
Click to expand...
They are keeping the pH too low and the TA too high.

Drop the TA and raise the pH and the amount of acid required will drop from 15 gallons per month to about 5 gallons per month or less.

You can also switch to CO2 for pH control and the TA will not drop using CO2.

Calcium hypochlorite is also part of the problem.

Switching to sodium hypochlorite or SWG would be a better choice than calcium hypochlorite.
 
A commercial pool probably has an upper limit of 7.8 for the pH.

If there was no upper limit defined, I would consider going up to as high as 8.3 for the pH because the higher the pH, the lower the percentage of bicarbonate that converts to carbon dioxide.

For example, there is about 16.5 times more CO2 at a pH of 7.0 compared to a pH of 8.3.

The TA range is probably also defined, which can make balancing challenging.

If the TA was defined to a high number and the pH to a low number, then I would consider using carbon dioxide for pH control.

pH....................%CO2
7.0........................18.292
7.1........................15.097
7.2........................12.377
7.3........................10.088
7.4........................8.183
7.5........................6.611
7.6........................5.324
7.7........................4.275
7.8........................3.426
7.9........................2.741
8.0........................2.189
8.1........................1.747
8.2........................1.392
8.3........................1.109
 
ETichansky said:
I'm honestly not sure, were you able to view the report that I uploaded?
Click to expand...
Yes.

The only significant component was calcium, which is expected.

It does not identify the major constituents of the scale.

You need to know the major constituents of the scale.

Contact the lab and ask them what the total composition of the scale is.

26% calcium does not tell us enough information.

I suspect that the majority of the scale is probably calcium carbonate and probably calcium phosphate, but you need to ask the lab why they did not fully analyze the sample.


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