Scale Developing on Waterline Tile within 1/2 Year Despite Negative CSI

DavidArmenB

Well-known member
Sep 7, 2022
262
Santa Clarita, CA
Pool Size
16500
Surface
Plaster
Chlorine
Salt Water Generator
SWG Type
Hayward Aqua Rite (T-15)
I did a complete rebuild of my pool in June. Removed the old plaster, all the tile, and the coping, and replaced it with Mini Pebble, Glass Tile, and Stamped Concrete Coping. So it is only seven months old.

I tested my fill water before filling:
All tests done with Taylor K-2006
June 12, 2023 - 7:30am
Temp: 74f
pH: 7.6
Total Alkalinity: 180ppm
Calcium Hardness: 180ppm
Salt: 410ppm (Digital Meter)
CSI: 0.16

I don’t know if this matters, but the water hardness here is also very high, at 16 grains per gallon (274ppm).

The fill process was the only time my pool had positive CSI. I followed the National Plasters Council New Plaster Start Up Guide so I brushed the entire surface multiple times a day for 7 days and then once a day for about a month while slowly balancing the water.

The Calcium Hardness rose to 220ppm after a few days due to the plaster dust and then up to 300ppm after about two months, it has stayed at 300-325ppm ever since. In that time, I had the Total Alkalinity reduced to 80ppm by slowly adding Acid to reduce the pH to 7.2 and then aerating until it rose back up to 7.8-8 and repeating, and I slowly brought the CYA up to 80ppm for my SWCG (I waited 8 weeks before adding salt and turning on the SWCG).

Here’s a test result about 6 weeks after plaster:
July 20, 2023 - 8:00am
Temp: 84f
FC: 9ppm
pH: 7.7
Total Alkalinity: 80ppm
Calcium Hardness: 300ppm
CYA: 50ppm
Salt: 710ppm
CSI: -0.09

Those values have stayed more or less the same with the exception of higher CYA and Salt.

Test result from today. This is very typical to what my numbers have been ever since I completely balanced the pool by early August 2023.

January 25 - 9:40am
Temp: 53f
pH: 7.9
FC: 8.4ppm
TA: 80ppm
CH: 325ppm
CYA: 60ppm
Salt: 3,000ppm
CSI: -0.17

In the summertime, I run a pH of 7.6 to keep CSI negative since I have my CYA at 80ppm, and my water temp reaches as high as 86f. Could it be that when pH temporary climbs above 7.6 and before I reduce it with acid, that is enough time for scale to form like this??

Typical summertime chemistry:
Temp: 86f
pH: 7.6
TA: 80ppm
CH: 325ppm
CYA: 80ppm
Salt: 3,000ppm
CSI: -0.19

Despite this, my glass tiles have developed scale, mostly starting around the grout lines and spreading from there:
IMG_2746.jpegIMG_2749.jpegIMG_2748.jpegIMG_2747.jpeg

It’s worse at the spa water line (pictured), where the water level is periodically higher when the spa is in spillover mode and then lowers to the standard level when spillover turns off.
 
Last edited:
Your pictures are not showing but I suspect you have Efflorescence - Further Reading coming out from your grout lines and not scale.

CSI does not effect efflorescence.
I have seen this phenomenon before! Looking at some example photos specifically with tile, I suspect my issue could possibly be efflorescence.
 
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