Dark spots forming in new white plaster

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Maintain the total chlorine at about 10% of the CYA reading and do an OCLT to verify that the chlorine level is adequate.

If you do not pass the OCLT, increase the total chlorine to 15% of the CYA and do another OCLT.
 
JamesW said:
Maintain the total chlorine at about 10% of the CYA reading and do an OCLT to verify that the chlorine level is adequate.

If you do not pass the OCLT, increase the total chlorine to 15% of the CYA and do another OCLT.
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ugh, ok, thanks again. Sounds like I'll have to add a lot of chlorine.
 
Don't use calcium hypochlorite and don't add a lot of chlorine at one time.

Do not allow any concentrated chlorine to reach the pool walls or floor.
 
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Here you can see how calcium hypochlorite makes a black copper staim.

They use aluminum sulfate to remove the stain, but I have never heard of that being used before, so I do not know how well it works.

It seems to work in the video.

Other possible stain removers are ascorbic acid, oxalic acid and citric acid.

Some might work, some might do nothing and some might make things worse.

 
Cupric oxide has copper in the +2 oxidation state and metallic aluminum can act as a reducing agent by providing electrons to the copper to convert it into copper metal, but aluminum in aluminum sulfate is already fully oxidized in the +3 state, so I am not sure what reaction is happening to remove the copper stain.


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This might be the reaction of aluminum sulfate and the copper (II) Oxide.

Al2(SO4)3 + 3CuO --> Al2O3 + 3CuSO4

Aluminum sulfate + Copper (II) oxide --> Aluminum oxide + Copper sulfate.

Aluminum oxide is usually white, so, if the copper oxide is becoming aluminum oxide, it might be a white stain, which will be ok for a white pool but it might be bad for a darker color plaster.

Darker plaster usually hides copper stains as long as the stains match the plaster color.

Some plaster is a turquoise, blue or green and that hides turquoise copper stains.

Darker grey or black plaster can hide grey or black copper stains.

Using aluminum sulfate on dark plaster might leave a white stain that looks worse than the darker stain.

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JamesW said:
Don't use calcium hypochlorite and don't add a lot of chlorine at one time.

Do not allow any concentrated chlorine to reach the pool walls or floor.
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ok, thanks. I have only ever used 10% liquid chlorine. One other question, what am I waiting for? How will my chlorine eventually go back to normal? I am a little worried bc I am in MD and do not have a lot of time left in the season.
 
The sulfamic acid acts like cyanuric acid where the chlorine connects to the nitrogen by substituting for a hydrogen ion.

This forms a compound that tests as CC.

The nitrogen eventually gets oxidized, which causes the sulfamic acid to go away.

This is similar to chlorine reacting with ammonia to form CC.

Chlorine tends to combine with nitrogen in the -3 oxidation state, but it also eventually oxidizes the nitrogen.

The rate of oxidation depends on the stability of the molecule.

Cyanuric acid and sulfamic acid are more stable than ammonia because they have bonds with other atoms.

Sulfamic acid has sulfur atoms bonded to the nitrogen and cyanuric acid has carbon atoms bonded with the nitrogen.

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The chlorine has an equilibrium with the sulfamic acid, so you should have some active chlorine (HOCl + OCl-) in the water, which is similar to how chlorine works with cyanuric acid.

5 lbs of sulfamic acid will increase the sulfamic acid level to 22 ppm.

If this works like cyanuric acid, then you would need about 2.2 ppm of total chlorine to have a 10% ratio of chlorine to sulfamic acid.

You would also need the same percentage with the CYA.

If the CYA is 75 ppm, then you need 7.5 ppm chlorine.

So, that puts you target total chlorine at about (7.5 + 2.2) = 9.7 ppm.

Over time, you should notice the CC levels going down as the chlorine oxidizes the nitrogen in the sulfamic acid.
 
JamesW said:
The chlorine has an equilibrium with the sulfamic acid, so you should have some active chlorine (HOCl + OCl-) in the water, which is similar to how chlorine works with cyanuric acid.

5 lbs of sulfamic acid will increase the sulfamic acid level to 22 ppm.

If this works like cyanuric acid, then you would need about 2.2 ppm of total chlorine to have a 10% ratio of chlorine to sulfamic acid.

You would also need the same percentage with the CYA.

If the CYA is 75 ppm, then you need 7.5 ppm chlorine.

So, that puts you target total chlorine at about (7.5 + 2.2) = 9.7 ppm.

Over time, you should notice the CC levels going down as the chlorine oxidizes the nitrogen in the sulfamic acid.
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bc of some heavy rain, my CYA is closer to 60, so I will shoot a little lower (8.2). Any way to know how long this will last? Bc this will require adding a significant amount of liquid chlorine. I don't quite understand why the SWG could make plenty of chlorine before, and now cannot seem to make near enough.
 
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Sumthinred said:
Any way to know how long this will last?
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Not really.

The higher the chlorine level, the faster the sulfamic acid will break down, but it also increases the risk of new copper stains.
Sumthinred said:
Bc this will require adding a significant amount of liquid chlorine.
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Not really, the total chlorine required is actually lower than if you had zero CYA and zero sulfamic acid.
Sumthinred said:
I don't quite understand why the SWG could make plenty of chlorine before, and now cannot seem to make near enough.
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Most likely, the levels got behind, which allows algae to get started even if you cannot see it yet.

Once you can pass the OCLT, the amount of chlorine required per day should level off to a level that the SWG can provide.
 
JamesW said:
Not really.

The higher the chlorine level, the faster the sulfamic acid will break down, but it also increases the risk of new copper stains.

Not really, the total chlorine required is actually lower than if you had zero CYA and zero sulfamic acid.

Most likely, the levels got behind, which allows algae to get started even if you cannot see it yet.

Once you can pass the OCLT, the amount of chlorine required per day should level off to a level that the SWG can provide.
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So the chlorine issue worked itself out, but our new pool is still stained and blotchy everywhere, and now the areas where I spot treated are dusty every time I brush, or put the vacuum in. They are whiter than the rest of the pool, but a dust always comes off when I brush. At first I thought it was just the Jacks #2 settling back on those spots, but I have since manually vacuumed and it hasn't stopped. Could I have damaged my plaster by using the stain treatment?
 
Sumthinred said:
our new pool is still stained and blotchy everywhere, and now the areas where I spot treated are dusty every time I brush, or put the vacuum in. They are whiter than the rest of the pool, but a dust always comes off when I brush.
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Sumthinred said:
Could I have damaged my plaster by using the stain treatment?
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Maybe, if you didn't follow the directions and you let it sit on a spot.

The plaster is white, so if you have general staining and you only treat a spot, then that spot will look different.

You probably should have done the whole pool instead of just a spot.

You probably dumped the product in a spot and let it sit, which is not what the directions say.

Also, as I noted, any treatment can have adverse effects, so you make an informed decision and assume the risk.

Maybe contact Jack's and see what they say.

Sumthinred said:
our new white plaster
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JamesW said:
Note that any treatment can have a bad reaction, so you have to do this at your own risk with no guarantee of it producing the desired effect and it might even have adverse effects.
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JamesW said:
Maybe, if you didn't follow the directions and you let it sit on a spot.

The plaster is white, so if you have general staining and you only treat a spot, then that spot will look different.

You probably should have done the whole pool instead of just a spot.

You probably dumped the product in a spot and let it sit, which is not what the directions say.

Also, as I noted, any treatment can have adverse effects, so you make an informed decision and assume the risk.

Maybe contact Jack's and see what they say.







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I spoke with someone from Jacks. He said what I am describing is scale. And the dark spots probably iron (and with the green water right after filling, assumed we had some iron anyway). He said the dusting of the plaster is normal.
 

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