2-year old Luna Quartz plaster chlorine pool with rising calcium and high pH

aaronk

Member
Aug 15, 2019
15
Dallas, TX
Hey guys, I'm a first-time pool owner, and we've had it since December 2016 (construction completed). We've had ongoing issues with high calcium, even though the water source in my town is only 160 CH. I also can't seem to keep the pH at my desired level of a 7.4. These may be two separate issues, but hopefully someone has insight.

It's a 20,000 gallon pool with a spa, and the plaster is Luna Quartz. Let's start with the calcium problems. When it was first built, we had TONS of plaster dust, and the builder gave it two acid baths to try to resolve the problem. Calcium was at a 480 when they ended their complimentary maintenance in March 2017. Over the next two years, we had all kinds of scale and calcium nodules form on the plaster.

This past May (2019), the pool was drained the first time by the builder, and they performed an acid wash to remove the scale and calcium nodules. After refilling, the calcium was still very high and acid wash not properly done. That led to the builder doing an acid bath and draining it again in June. Upon refilling, the CH was tested at 160 (same as tap water), so I added calcium to bring it to a 220. So far, so good.

By July, just one month after refilling it the second time, I noticed the CH had already climbed to a 320. Given that cal hypo shock contains calcium, I thought possibly the shock was causing the problem. I stopped using cal hypo and switched to liquid chlorine a few weeks ago. The calcium seemed to stay steady at 320 for a couple weeks, but on my last test a few days ago it had climbed to a 350.

The other thing that I cannot seem to keep steady is the pH. Even when the water is perfectly balanced and the LSI is at a 0.00, within a 24 to 48 hours, my pH will go from a 7.4 to 7.8 or 8.0. I'm having to add 4 to 6 cups of muriatic acid almost every other day to keep the pH back down to a 7.4. (The reason for keeping it at a 7.4 is to keep my LSI as close to 0 as possible. At a 7.8 or 8.0, the LSI is at a +0.4, and I'm concerned about having more scale and calcium deposits.)

1. What might be causing my CH to rise?
2. Why can't I keep my pH steady?

Here are my numbers as of today:
Temp: 93 degrees (it's hot in TX right now)
pH: 7.6 (added 6 cups of MA yesterday to bring it down to 7.4, and it's already back up to 7.6)
Alkalinity: 100
CYA: 40
Chlorine: 2.0 (also added about 1/2 gallon of liquid chlorine yesterday, which I know has high pH)
 

sktn77a

Gold Supporter
May 16, 2010
1,364
Chapel Hill, NC
Try letting you TA drop to ~60. That should help with the pH issue. Not sure why your CH is increasing so fast. I hope it's not because the PB has burned through the hard plaster surface, with all those acid baths, and exposed the softer plaster underneath(?)
 
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Rocket J Squirrel

Bronze Supporter
Jun 7, 2018
516
Alamo, CA
I also have Luna Quartz. I also have high CH at 370. But it’s stable so I don’t care. Why do you care? Maybe our plaster’s CH sweet spot is simply high. Lowering it might only cause more calcium to dissolve into solution.

I would leave it alone and see whether it stabilizes. If it does, relax. If it continues to rise forever, you have cause for concern.
 

aaronk

Member
Aug 15, 2019
15
Dallas, TX
The high CH wouldn't be as bothersome if I didn't have a problem with scale and calcium nodules forming on the plaster. Also, the pH does not like to stay at ~7.2-7.4, so when coupled with high CH, that has caused me problems.

Do you also have high pH with your Luna Quartz?
 

Rocket J Squirrel

Bronze Supporter
Jun 7, 2018
516
Alamo, CA
Oh, sorry, I missed where you said you had scale and nodules.

My pH rose constantly when the plaster was fresh, but is stable now despite my high TA (120). I add MA about every 2 or 3 weeks. @sktn77a might have the right idea, that all that acid exposed another layer of plaster.
 

ScottinTX

Member
Oct 20, 2018
24
Ft. Worth, TX
How much CH is in your fill water? If your fill water is not softened, you're adding CH every time you add water to keep up with evaporation. I'm in the Ft. Worth area and lose around 100 gallons per day from evaporation.
 

aaronk

Member
Aug 15, 2019
15
Dallas, TX
I tested our tap water at 160 CH. If evaporation and fill water were the problem, I'd think my neighbors would all have the same issue. I've asked, and they don't have problems nor water softeners.
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
22,396
Laughlin, NV
No. I have higher CH fill water and manage it by monitoring CSI. When our CH hits 800+ppm I exchange the water to fresh.

You get rain, so should be able to manage it that way.
 

CaveDiver1932

Well-known member
Mar 2, 2014
97
Dallas
No. Dallas water sourced by lakes and that is not hard water.
When the pool was drained did you notice any hollow plaster areas? Hollow plaster is a big source of calcium nodules. Your fill water is in a sweet spot
 

aaronk

Member
Aug 15, 2019
15
Dallas, TX
I suppose it's possible the calcium nodules were coming from the plaster, but doesn't it seem more likely they were forming because of the high CH and pH (falling out of solution)?

At one point my CH had reached 520 (prior to the acid wash and refill). The nodules could be scraped off with my fingernail, and it didn't look like there were any cracks below the nodule. I've seen photos of calcium deposits that leached from the plaster, and that's not what mine looked like. After the acid wash, the plaster looked fine. I did, however, notice two very long hairline cracks on the wall below my spa waterfall/spillover. They are probably 5 feet long, but again, they are hairline and (according to an independent pool professional--not the builder) cosmetic in nature.
 

CaveDiver1932

Well-known member
Mar 2, 2014
97
Dallas
IMO. Your runaway ph most likely likely is opposite of what you are thinking. If I read your post correctly (read very fast), it appeared the calcium or calcium nodules where bad like all over the pool. This most likely means calcium hydroxide is leaching through the voids and when it comes in contact with the alkalinity in the pool water it creates calcium carbonate which forms the nodules. The calcium hydroxide has a high ph which causes the water ph to rise.

Acid wash is a temporary solution as long as calcium hydroxide is still leaching through the voids. I don’t believe there is anything you can do with water chemistry to stop this from happening.

Is the pb blaming your water chemistry for your issues?
 
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aaronk

Member
Aug 15, 2019
15
Dallas, TX
The builder initially blamed my water chemistry, but eventually they agreed to do the acid bath and admitted it may have been caused by improper startup (lots of plaster dust and very high CH from day 1). It seems that every pool person I've talked to about this has a different answer. There really has been no consistency, even between different people who work for the pool builder. I get a different explanation every time I try to get to the source of the problem, which leaves me more confused than when I started and no closer to figuring it out.

I don't have any nodules at the moment, and I haven't had any since the acid wash and refill. This is probably in part because I've been testing the water every couple days, and I've been very diligent about keeping it perfectly balanced. But I'm adding 4 to 6 cups of MA almost every 48 hours, and that seems pretty excessive to me.
 

CaveDiver1932

Well-known member
Mar 2, 2014
97
Dallas
I’m sorry to hear this. It seems as I describe and not an issue you created.
@onBalance can possibly confirm and offer away to approach your pool builder.

If I read correctly this was a new pool and not a replaster/remodel? New pool is a tad puzzling. This issue is normally resulting from bad prep found in remodels. High calcium hardness up in 800 can be maintained without issues as a reference point for example of not the cause of nodules.

Cd
 
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aaronk

Member
Aug 15, 2019
15
Dallas, TX
Yes, we built the pool in late 2016. To give you an idea of what I'm up against, here's my water test log from the past week.

8/10/2019
FC: 2.0
pH: 7.5
TA: 110
CH: 320
CYA: 40

8/11/2019
FC: 1.0
pH: 7.8
TA: not tested
CH: not tested
CYA: not tested
***added 1/2 gallon 10% liquid chlorine & 5 cups muriatic acid

8/12/2019
FC: 2.0
pH: 7.7 (morning) / 7.4 (evening, about 4 hours after adding acid)
TA: 100
CH: not tested
CYA: not tested
***added 1/2 gallon 10% liquid chlorine & 4 cups muriatic acid

8/13/2019 - no tests run

8/14/2019
FC: 2.0
pH: 7.8 (morning) / 7.2 (afternoon, about 4 hours after adding acid)
TA: 100
CH: 350
CYA: 50
***added 6 cups muriatic acid

8/15/2019 - drained about 1/3 of my pool and refilled with fresh water

8/16/2019
FC: 4.4 (added 1 gal. liquid chlorine in morning, tested in afternoon)
CC: 0.0
pH: 8.0 (afternoon test) / 7.4 (evening test after adding acid)
TA: 80
CH: 310
CYA: 40
***added 6 cups muriatic acid in afternoon

8/17/2019
FC: 2.2 (added 1 gal. liquid chlorine in morning, tested in afternoon)
pH: 7.8 (afternoon test, a few minutes ago)
TA: not tested
CH: not tested
CYA: not tested
***added 1/2 gal. liquid chlorine & 6 cups muriatic acid
 
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