Anyone know what this is and more importantly how to get rid of it?

kissem

New member
Jun 6, 2015
4
south shore/Ma
#1
Hi all,

I'm located in the northeast and I had a gunite salt water 18x36 free form pool installed and ready for swim in late August 2015. It has a dark grey plaster finish. Last year we had no problems. I took the cover off this year and this is what I discovered. I've brought these pics to the local expert pool place and 3 of them said they've never seen this before. I brushed on some 50/50 MA mix and it foamed up so I believe it's calcium build up of some sort. The pool guy didn't understand how this could be because the calcium readout was almost zero. I tried brushing with a wire brush and the stuff just barely comes off. It feels like 60 grit sandpaper. The pic labeled pool step is of the sun shelf that was not underwater during the winter compared to the greenish brown step that was underwater. The entire pool looks to be coated with this stuff. My test results are PH: 8.6, hardness: 45, TDS: 1400, Free Chlorine: 0.1, Total chlorine: 0.1, CYA: 5, Optimizer plus: 2. Any ideas on what this is, how to prevent it, and how to remove it would be much appreciated.
 

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Richard320

TFP Expert
LifeTime Supporter
Jan 6, 2010
20,328
San Dimas, CA (LA County)
#4
By description that's Calcium Scale. It could be salt, though, mixed with some Calcium. Odds are the water you tested is the upper layer from rain and snowmelt, so it's going to read really low. Figure out a way to grab a sample from the bottom. Maybe duct tape a water bottle to the pool pole at an angle so it holds trapped air until you turn it upright to grab a sample from deep. See what that water reads.
 

duraleigh

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Mod Squad
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In The Industry
Apr 1, 2007
31,387
Sebring, Florida
#5
I think you can safely assume you have Calcium scale. The high, high pH of the water created a perfect environment.

1. Drain and acid wash

2. No drain acid bath

3. Lower pH to about 7.0 and dissolve scale.

Those are about your only choices. The most aggressive and effective is to drain and acid wash......it removes some of the good plaster with it, however

The no-drain acid bath is not used very often but, technically, there is no reason not to do it.

Lowering your pH and keeping it there is the safest but can take months to see much affect.
 

woodyp

Mod Squad
TFP Expert
LifeTime Supporter
Apr 17, 2010
10,227
East Texas
#6
Given that there is dang little to no calcium in that pool---------is the high, high PH eating the pool finish itself or drawing the calcium out of the plaster?
 

pooldv

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Aug 10, 2012
24,993
DFW, TX
#7
I would say more likely that the CH was removed from the water and deposited on the walls as scale.
 
OP
OP
K

kissem

New member
Jun 6, 2015
4
south shore/Ma
#9
So I called around for companies that do acid washes. The one guy I talked with said it sounded to him that the water, due to the low calcium count, pulled the calcium out of the plaster. He said an acid wash won't fix the problem because the plaster will still be rough and suggested painting it. Research on paint is that at best it lasts 7-8 years. At this point I'm more inclined to do the no drain acid bath.