Can high CYA cause plaster spotting?

[cardude]

Quick intro. I'm in south Tx. 45000 pool. Pool is 3 years old. Plaster.

Recently I have been getting dime sized spots in my plaster all over the pool. They seem to be rougher than the rest of the plaster. The pool looks like polka dots now. My cya was very high at 260 until I did a couple of partial drains an refills. The rest of the numbers were always pretty much in range.

Here are my current numbers using a Taylor 2006 kit. Chlorine.

Cya 60
Calcium hardness 200
TA 170
FC 5.5
CC .4
Ph 7.4

I switched to the bbb chemical method recently. Water looks great but the dots worry me.

 

[Richard320]

No. But if CYA dropped 75%, so did CH. And if it's 200 now, it could have been 800. It's probably Calcium Scale. What color are the spots? If they're tan or blue-grey, it's probably Calcium. If they're white, it's more likely the whole pool has scale and the spots are where it's the plaster underneath.
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Does your pool look like this? This was the floor of my spa. It's now almost all white, after almost two years of trying to dissolve scale.

 

[cardude]

It looks exactly like that. The spots are rough like the plaster has been eaten up on these spots.

Is there a fix?

Thanks

 

[Richard320]

It looks exactly like that. The spots are rough like the plaster has been eaten up on these spots.

Is there a fix?

Thanks

Sounds like you are experiencing what I surmise happened to my pool: It got a nice, even coating of scale, then they tossed some sort of granular shock in to beautify the thing when the house went on the market. Where the granules landed, they dissolved the scale and some of the underlying plaster.

My fix has been to be obsessive with my testing and keep pH low during the non-swim season and brush with a wire brush. I also grab every bit of rainwater I can and pump out to water the lawn then refill to reduce the Calcium. It's a long, slow process. progress-on-scale-t38568.html

 

[onBalance]

Cardude, your water may have been aggressive in the past due to the high CYA, but that may have been partially offset by high calcium hardness. If your spotting problem is also occurring on walls, that would indicate that the spotting would not be the result of some granular material being added.

Recent cement analysis has shown that a certain type of "white spotting" is actually from improper plastering practices. The spots are very porous compared to the surrounding plaster surface. These spots have lost cement material (up to 3 or 4 millimeters deep creating a very porous spot) over time due to the weakness caused by improper plastering. They can turn tan or turquoise from various metals depositing in to the porous spots.

Plasterers often call those spots "spot etching" because they think it is caused by aggressive water, but they are wrong. Aggressive water WILL make the spots appear sooner and be more rough to the touch, but doesn't cause the problem. If the plastering is done correctly, aggressive water would cause uniform etching, not in isolated spots. In time, the spotting will begin to show even in balanced water. Improper plastering creates some SOLUBLE cement material, which results in water natually dissolving it away over time.

 

[cardude]

After looking at the picture richard320 posted again, I don't think that's what mine looks like after all. My spots are more what onblalnce described-- dime to quarter sized porus spots all over the pool. My pool builder is sending his guy by to look, and I'm sure he will blame it on aggressive water.........

Would high TA cause etching like this?? Buy why would it do it in spots and not all over??

I retested today and it looks like this:
FC 4.2 CC 0 (added some bleach to get this back up to 6)
PH 7.4
TA 180
CH 200
CYA 60-70

 

[cardude]

http://www.cmc-concrete.com/CMC%20Semin ... ations.pdf

This article suggest possible excess trichlor use and high CYA levels could cause spotting. I did use lots of the trichlor tabs, which caused my high CYA. Is this valid?

The article also says it could be poor plastering technique..........

:?: :?: :?: :?:

 

[onBalance]

High TA (and/or high calcium hardness) leads to scaling, which is just the opposite of etching which is caused by aggressive water (low TA and low calcium hardness).

You are right that imbalanced water causes uniform issues, not in spots (unless something granular like dry acid sits on the plaster. The problem with the referenced (cmc-concrete) study you mention is that an older plaster pool was apparently used for the study, and that particular pool had a spotting problem in addition to an overall etched surface. Also, that researcher based the possible high CYA and excess trichlor issues on another study perform by Cal Poly University, which also involved the plastering industry performing the work and over-seeing the project. That study was flawed. So the researcher would not rule out aggressive water. And interestingly, his study also included the participiation of seveal plasterers.

Had the researcher looked at a newer and smoother plaster pool with spotting, he probably would have a more definitive conclusion regarding poor plastering practices.

 

[onBalance]

Cardude, I forgot to answer your question about whether the "white spotting" can be fixed. The answer is no. Those porous soft spots cannot be reversed, which is unfortunate. Adjusting the water chemistry will not make a difference to that type of spotting. The plasterer may suggest an acid wash, but that will not work and will only make your entire plaster job older and rougher overall. Sorry for the bad news. And just clarity, the above mentioned studies DID NOT prove that a high CYA causes any type of spotting. No study has proven that, and no study has proven that aggressive water causes white spotting.

And one more thing. You stated that your spots are rougher than the rest of the plaster surface. Another possiblility of a white spotting problem is due to calcium nodules, which are small around raised calcium deposits on top of the plaster surface. They form along cracks in the plaster. There might be a delaminating problem. So you should inspect very close to determine which it is.