3 month old new plaster pool with grey/blue dots

DMC2010

Member
Aug 28, 2019
6
West Chester, PA
New plaster pool build here 1 year ago, was replastered upon opening this Spring (long story, main drains were leaking and drilled out/repaired). Now, 3 months after new plaster, we are noticing these grey dots/spots on the plaster on the walls and floor of the pool in addition to tiny black specs. We noticed it more after shocking although that may have been coincidental. We just used pool magnet plus per the retail store with no results. Also, starting to notice these bright white areas as well. Any advice?
 

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JamesW

TFP Expert
Mar 2, 2011
16,353
Maybe copper. Have you ever used anything with copper in it?

Try ascorbic acid (vitamin C)on a spot.

Are you using calcium hypochlorite?
 

DMC2010

Member
Aug 28, 2019
6
West Chester, PA
We haven’t ever used anything with copper in the pool. Also, forgot to mention the spots do not scratch off at all. The retail store tested for copper and none showed in the results. Yes we use calcium hypo shock and we have a standard chlorinator.
 

JamesW

TFP Expert
Mar 2, 2011
16,353
I would avoid calcium hypochlorite. I suspect that granules are reacting with metals and the plaster.

Do you have a heater?

Do you have an ionizer?

Have you ever used algaecide?

Put some vitamin C on the spot to see what happens.
 

DMC2010

Member
Aug 28, 2019
6
West Chester, PA
We do have a heater and attached spa (handy pro series gas-fired heater). We have a chlorinator and a DE filter. No ionizer. We use Burnout 3 Granular Shock. We use muriatic acid to lower the PH as needed. We have added calcium to raise the calcium level (low levels on testing) because of new plaster per the retail store. We have added Omni total alkalinity increaser (sodium hydrogen carbonate) at times. No additives appear to contain anything that says the word blue. Has anyone seen this before? Hoping to rectify the issue prior to closing.
 

JamesW

TFP Expert
Mar 2, 2011
16,353
Do you have a picture of the system?

Is the tab feeder near the heater?

Is the pump ever off while there are tabs in the feeder?

Did you do the vitamin C?
 

skimmerswimmer

Well-known member
Jul 30, 2013
334
Long Island, NY
When I had my pool replastered, I had a spot where the plaster had tiny dark area that wouldn't come off. Turns out there was a tiny stick embedded under the plaster that started to decompose and leech out. A wire brush eventually pulled off enough of the plaster for me to remove the stick, but the side of my pool still has the scar. Your issue may be completely different, but I found that it helps to keep the PH low (7.0 - 7.2) for the first year to ensure you don't get a lot of calcium buildup and the residual "cream" comes off and exposes the aggregate.
 

JamesW

TFP Expert
Mar 2, 2011
16,353
If the tab feeder has tabs inside while the pump is off, chlorine will migrate into the heater and cause corrosion.

I would never leave the pump off when the feeder had tabs inside.

In any case, I think that the spots are most likely copper stains precipitated by calcium hypochlorite granules making contact with the plaster.

I would discontinue the use of calcium hypochlorite.

You can try some sulfamic acid on the spots if you want. Jack's #2 copper and scale stuff is sulfamic acid.

Sulfamic acid will lock up the chlorine for weeks. Maybe just spot treat to minimize the amount of sulfamic acid needed.

The white spots are likely what's referred to as "spot etching".

Some plasterers say that "spot etching" is due to poor water chemistry. But, if the chemistry was etching the plaster, it would do so evenly.

Spot etching is the result of plaster application problems.


 
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DMC2010

Member
Aug 28, 2019
6
West Chester, PA
Thanks for your response. So in regards to the chlorinator, the pump is set to run for 12 hrs on/off. We always keep tabs in the chlorinator. Do you recommend “closing” the chlorinator by turning the dial every time the pump turns off and turning it back on when it restarts? I had no idea about this.

Are there any “side effects” of the Jacks #2 that you recommended? This product is an attempt to rid the pool of these spots and not just prevent new ones, correct?
 

JamesW

TFP Expert
Mar 2, 2011
16,353
I don't like tab feeders at all. If there is no flow, the tabs continue to dissolve and you get a very toxic, corrosive liquid and gas mixture that begins to migrate through the system destroying everything it touches.

If you have ever opened the feeder and been exposed to the gas, you have an idea about what I mean.

I would not ever leave the pump off when there are tabs in the feeder.

I'm not recommending the Jack's #2. I'm saying that it might work for you.

Sulfamic acid is somewhat similar to cyanuric acid in that it combines with chlorine to form a stable chlorinated molecule.

If you use it, it will make any chlorine read as CC for weeks or months.

You can try doing an ascorbic acid treatment, but it doesn't always work on copper and it can even make things worse.

Using a sequestrant and careful management of the chemistry can help reduce further stains but there's no guarantee.