Black stains just keep getting worse

[Rich G]

So I drained the water down to the shelf again to expose some of the stains and treat them again. After soaking in LC all day yesterday the stains are disappearing again. I cannot get any residue or anything when scraping at these

 

[ajw22]

So I drained the water down to the shelf again to expose some of the stains and treat them again. After soaking in LC all day yesterday the stains are disappearing again. I cannot get any residue or anything when scraping at thrse

LC being effective points to the stains being organic and likely black algae roots in your plaster.

How old is your plaster?

You may have this occuring until you replaster the pool.

 

[JamesW]

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How White Pool Plaster Turns Blotchy

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Procedure to adress Hydration (plaster discoloration)

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Hydration Stains?

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Gray Mottling Plaster Discoloration

Gray (also spelled “grey”) or darkened blotchy or streaky discoloration of pool plaster (cement flatwork) is known to be caused by several improper plastering practices, including the addition of calcium chloride to the mix (even less than 2%), late hard or dry troweling, and sometimes a cement...

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Stubborn stains and discoloration in new quartz plaster pool

Hello all decided to finally join after being along time lurker before deciding to build new pool. My pool was plastered in Sep 2021 with quartz plaster. Everything began as expected and start up was performed by builder via traditional bicarb start up. Everything looked amazing and perfectly...

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[JamesW]

I don't think that it is black algae, but I don't know exactly what it is.

Have you tried sulfamic acid?

Have you done a copper test?

 

[Rich G]

LC being effective points to the stains being organic and likely black algae roots in your plaster.

How old is your plaster?

You may have this occuring until you replaster the pool.

Plaster was new in 2017 so about five and a half years. I want to believe it’s algae but never once been able to get a color off these stains and everything I read says I should get green or black residue. I am afraid it will keep occurring which is really disappointing.
I had a pool guy come by and guarantee me they were organic stains… I just don’t get why I don’t get any residue when I scrape or pick at them

I don't think that it is black algae, but I don't know exactly what it is.

Have you tried sulfamic acid?

Have you done a copper test?

I have tried sulfamic acid, I even did the jacks treatment and it made almost no difference from what I can tell.. all my copper tests are low and I’ve never added any weird chemicals.

 

[JamesW]

Your cartridges don't show blue/turquoise, which would indicate copper.

It might be a metal, but I really don't know what it is.

Maybe silver?

Maybe @onBalance will have some ideas?

 

[Bperry]

I’m still of the opinion you’re running your maintenance level of chlorine too low for your CYA.

 

[Rich G]

I’m still of the opinion you’re running your maintenance level of chlorine too low for your CYA.

I’ve had it in alignment with the chart or much higher since I cleaned these stains last time. That said, I’m gonna let these soak for another day or two and then run the FC levels at like 20 for a few weeks to cook these stains.

 

[onBalance]

I think we should consider that there might have been some bad (contaminated) plaster in the original plaster mix. I would also think that the plaster surface has etched significantly after all of the chemical treatments so far. Probably should have notified the plastering contractor about this discoloration in the beginning.
At this point, I suggest power sanding the top shelf to smooth the surface and perhaps might remove the discoloration. However, the contaminated plaster might be rather deep and impossible to remove.

 

[Rich G]

I think we should consider that there might have been some bad (contaminated) plaster in the original plaster mix. I would also think that the plaster surface has etched significantly after all of the chemical treatments so far. Probably should have notified the plastering contractor about this discoloration in the beginning.
At this point, I suggest power sanding the top shelf to smooth the surface and perhaps might remove the discoloration. However, the contaminated plaster might be rather deep and impossible to remove.

Interesting. I actually thought about taking some coarse sandpaper to the stains to see what happens.