Calcium Crystals? or Scale?

[cmdonnel]

I really need some expert help here please.
Quick backstory:
30K Gunite pool with Diamondbrite exposed agg finish finished in September 2020 near Philly Pa. SWG added Spring 2021. I've always maintained my own water chemistry using the Taylor test kits (full recent results to be posted below); also use the Orenda App and Pool Math to maintain CSI/LSI. Immediately after the pool was finished in 2020, the plaster was super rough and folks were cutting their feet playing sports in the pool. Finally filed a warranty claim in 2022 that was denied by pool builder (claiming it was water chemistry), so I paid to have the pool drained and "polished" (hand sanded using diamond discs) in the spring of 2023. New water was added and balanced. When I reopened the pool in spring 2024, I noticed calcium deposits all over the pool BELOW the water line. It was not scale, but calcium crystals that were razor sharp and all over the pool walls and floor. I tried lowering the TA and chemically removing them, but they could only be sanded off. So once again I hired a company to drain and "polish" the pool. All was smooth once again. I then did alot of research on CSI and LSI and made sure the CSI was between -.1 and +.1 all summer. Water was crystal clear and plaster was smooth. In an effort to not repeat the calcium crystals I decided to attempt balancing the water over the winter to rule out water chemistry as the cause of the crystals. I dropped 4 sump pumps with directional PVC pipes throughout the pool to create a circular "flow" and have been checking the water ever week since the closing on Nov 4, 2024. The water chemistry has been stable with the number I will post below. Unfortunately, with my latest weekly check I've noticed that the calcium crystals are just starting to return! Some folks now say the CH is too high, others say its too low.. but the CSI has remained between -.3 and +.3 since closing using pool math. Please help! Any advice is appreciated!

Current Pool Chemistry (numbers have been stable since closing, besides the water temp dropping):
pH: 7.8 (may be 7.7 as the color is a little lighter)
TA: 90
CH: 400 (may be 420, hard to tell some times with the exact color change)
CYA: 25
Water Temp: 38
Salt: 3100
No Borates

 

[JamesW]

Pictures?

 

[JamesW]

https://cpo.training/wp-content/uploads/2022/03/onbalance_ks_calciumscaleupdate.pdf

White crystals forming on plaster

I didn't notice these during the summer. I noticed using the spa this winter that something sharp like thorns was poking my legs. There are small and jagged white crystals stuck to the plaster in the spa. It's been too cold to see if they're in the pool as well. Is this salt or calcium or...

www.troublefreepool.com

The Mystery of the Pointed Crystals

Seemingly overnight, this pool was covered in sharp crystals. Where did they come from?

www.aquamagazine.com

 

[JamesW]

What do you use to lower the pH?

 

[ajw22]

Have you used dry acid in the pool?

Calcium Scale - Further Reading

www.troublefreepool.com

Calcium scale is normally from calcium carbonate but can be from calcium sulfate (CaSO4). Aqua Magazine:The Mystery of the Pointed Crystals describes a calcium sulfate scale situation. Orenda Understanding Calcium Sulfate Scale Crystals further describes calcium sulfate scaling and solutions for it.

 

[JamesW]

Sulphate Attack (TN3) - PWTAG - The Pool Water Treatment Advisory Group

PWTAG Technical notes are updates or new material for the standards and guidance given in the PWTAG book, Swimming Pool…

www.pwtag.org

PWTAG Technical Notes | Pool Water Treatment Advisory Group

PWTAG technical notes are updates or new material for the standards and guidance given in the PWTAG book, Swimming Pool Water.

www.pwtag.org

 

[JamesW]

3 – Sulphate attack

TECHNICAL NOTE

February 2011

An increasing number of reports have been received about problems being experienced in swimming pools due to the use of sulphate-based chemicals.

In most cases the initial effects observed are some erosion of the cement grout with a white suspension forming in the pool water when the grout surface is agitated.

In one case a hotel pool had a water supply with just over 6mg/l sulphate with balanced pool water but the use of sodium bisulphate (dry acid)and alum (sulphate-based salt) had raised the sulphate level to 1,582mg/l with erosion of the grouted joints quite evident.

The dangers of sulphate levels in pool water were highlighted by PWTAG in December 1987 following the recommendations given in BS 5385: Part 4: 1986.

The current edition of this tiling Code of Practice advises


Clause 7.3.1 General.

Ideally the sulfate concentration (SO3) of water in swimming pools should not exceed 300 mg/l.

Where greater concentrations of sulfates cannot be avoided, impermeable adhesives and grouting materials that are not affected by sulfates should be used.

High levels of sulfate would otherwise react with and erode materials containing Portland cement (CEM 1).

Clause 7.3.2.9 Pool water conditions

The use of sulfate containing chemicals, e.g. sodium bisulfate (dry acid), should be discouraged due to the need to keep sulfate levels as low as practicable and to prevent sulfate attack on cement grouts, tile beds, screeds, rendering and concrete.

The total dissolved solids (TDS) need not be high for sulphate attack to occur if sodium bisulphate is used in pool water.

Sulphate attack occurs under balanced water conditions, even at concentrations below the maximum recommended concentrations, but more slowly since the rate of attack is concentration dependent.

Note also that sulphate ions can migrate into the cement mortars, renders, screeds or concrete and begin to react.

However the effects will not be immediately evident as they manifest on the surface of mortars in contact with the pool water.

Where sulphate attack occurs on Portland cement mortars and concrete, the effects will not be as readily apparent, as in the initial stages the expanded reaction products fill up any pores or fine cracks within the mortar.

Once all the voids are filled the further growth of expanded reaction products starts to disrupt the cement mortar or concrete.

A classic example of this was where the first sign of a problem was when the tiles in the overflow channel of a freeboard pool tented due to expansion from sulphate attack and the adhesive beneath were found to have disintegrated.

Note that using sodium bisulphate to lower the pH of the pool water effectively adds an equimolar mixture of sodium sulphate and sulphuric acid to the pool water and for the same hydrogen ion concentration you are adding nearly 3.3 times more ‘dissolved solids’ to the pool water than if you added the equivalent amount of hydrochloric acid.

This means that using dilute hydrochloric acid has far less effect on the TDS of the pool water and, since the sodium bisulphate has to be dissolved in water, the amount of ‘liquid’ added to the pool should be less using dilute hydrochloric acid to control pH.

Note that dilute solutions of either hydrochloric acid or sodium bisulphate with the same hydrogen ion concentration are hazardous; however there is no need to use concentrated hydrochloric acid as hydrochloric acid is available in a range of concentrations for use in swimming pools.

As a result of the long-term experience with the effects of using sulphate based chemicals in treating swimming pool water, it is strongly recommended that the use of sulphate-based chemicals should be avoided in swimming pools of concrete construction, and where cement based renders, screeds, tile adhesives and grouts are present.

Carbon dioxide is a better alternative for many pools– but not if the supply water hardness is over 300mg/l, and not in leisure and spa pools where water features expel CO2.

CO2 does not raise TDS levels and so presents less of a risk of both grout erosion and general corrosion damage.

https://www.palmacademy.co.uk/opera...nload/pwtag-technical-note-3-sulphate-attacks

 

[JamesW]

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[cmdonnel]

Thanks for the quick replies! I will post pictures to a site and send the link.
I’ve only ever used muriatic acid to lower ph. No sulphate based chemicals that n aware of.
Liquid chlorine when needed… otherwise SWG.. and muriatic acid.

 

[ajw22]

I will post pictures to a site and send the link.

Please post pictures to the forum.

Picture Posting and Resizing - Further Reading

www.troublefreepool.com

 

[Bperry]

I really need some expert help here please.
Quick backstory:
30K Gunite pool with Diamondbrite exposed agg finish finished in September 2020 near Philly Pa. SWG added Spring 2021. I've always maintained my own water chemistry using the Taylor test kits (full recent results to be posted below); also use the Orenda App and Pool Math to maintain CSI/LSI. Immediately after the pool was finished in 2020, the plaster was super rough and folks were cutting their feet playing sports in the pool. Finally filed a warranty claim in 2022 that was denied by pool builder (claiming it was water chemistry), so I paid to have the pool drained and "polished" (hand sanded using diamond discs) in the spring of 2023. New water was added and balanced. When I reopened the pool in spring 2024, I noticed calcium deposits all over the pool BELOW the water line. It was not scale, but calcium crystals that were razor sharp and all over the pool walls and floor. I tried lowering the TA and chemically removing them, but they could only be sanded off. So once again I hired a company to drain and "polish" the pool. All was smooth once again. I then did alot of research on CSI and LSI and made sure the CSI was between -.1 and +.1 all summer. Water was crystal clear and plaster was smooth. In an effort to not repeat the calcium crystals I decided to attempt balancing the water over the winter to rule out water chemistry as the cause of the crystals. I dropped 4 sump pumps with directional PVC pipes throughout the pool to create a circular "flow" and have been checking the water ever week since the closing on Nov 4, 2024. The water chemistry has been stable with the number I will post below. Unfortunately, with my latest weekly check I've noticed that the calcium crystals are just starting to return! Some folks now say the CH is too high, others say its too low.. but the CSI has remained between -.3 and +.3 since closing using pool math. Please help! Any advice is appreciated!

Current Pool Chemistry (numbers have been stable since closing, besides the water temp dropping):
pH: 7.8 (may be 7.7 as the color is a little lighter)
TA: 90
CH: 400 (may be 420, hard to tell some times with the exact color change)
CYA: 25
Water Temp: 38
Salt: 3100
No Borates

Are you measuring CSI or LSI? Do you have logs of the water test results over the period since you polished the surface last?

 

[JamesW]

Test for sulfate.

 

[cmdonnel]

Hi James, What is best way to test for sulfate? Out of curiosity, how would the sulfate have gotten in there if I've never used sulfur based chemicals and the pool was tank filled (other than fill water)?

Bperry, I've been testing CSI using pool math and the OrendaApp. I do have a running log of all pool tests since the last fill. I will put them into excel and upload. I should have been logging everything in PoolMath, so that's my bad for not doing that. The results have been pretty steady though, with just the ph constantly increasing (due to the SWG). I add about 2 pints of muriatic acid a week. I kept the TA around 60 which slowed the ph Increase and then added TA increaser if it got to 50 (only had to do that once over the summer). Other than that, I just added Calcium once the pool was filled to bring it to around 350 and havent touched it since.

I went out today and took some pics of the current situation. I will attempt to post them here. Luckily the deposits can be brushed off at this point in time but I need to figure out what is causing them so I can stop the cycle. I also don't know how I'm going to brush them all off with the solid cover still on the pool. I fear if I dont brush them off now they will harden like last year and have to be sanded off again. I did take a video of the water flowing with the sump pumps running and you can see a bunch of the sediment floating around. You can also see some of the sediment that settled on one of the steps. I captured a couple and put them in muriatic acid and they disappeared immediately. Note - the water appears cloudy but I believe that is due to an overdose of Jacks Magic Purple Stuff during closing by the pool closing company. I've spoken with jacks Magic and they said the only side affect would be cloudy water, but I wanted to mention that in case it helps with the mystery.

I read through all of the articles above and do believe it is calcium carbonate. I've also been in contact with the Orenda folks since last year and they thought maybe the pool was too LOW on calcium, hence why I increased it to like 400 for this closing.

 

[cmdonnel]

Here are some pics from last April as well that show you how bad it got. The deposits almost "dripped" down the walls and were razor sharp. They were everywhere.. walls and floor and couldnt be brushed off at that point.

 

[JamesW]

Hi James, What is best way to test for sulfate?

Maybe a pool store or get a sulfate test kit.

Also, test for phosphate.

Put a drop of muriatic acid on some of the scale to see if it dissolves and bubbles, which would indicate calcium carbonate.

 

[cmdonnel]

Thank you, I see a couple sulfate test kits on amazon and will purchase one.
I did have the pool store test for phosphates.. they are "high" at around 3000, but I believe that is due to the Jacks Magic that was added right at closing. Prior to closing they were around 400.

I did do the "fizz test" today and they sediment dissolved immediately. Last year when I did the same test, it fizzed and then dissolved, but the piece I tested last year was bigger. But I definitely think its calcium carbonate. I just dont know how to control or stop it! Last year when this happened I was chatting with onBalance on this forum but unfortunately we hit a dead end on the investigation and I just had the pool polished again to remove them, hoping they wouldnt come back. I believe the issue may be with the plaster itself, but I need help ruling out everything else, and then building a case against the pool builder. It's also vey odd that it didnt first occur until after I had the plaster polished the first time to remove the over-aggregation. Could that have weakened the plaster and is now allowing calcium to be pushed through it?

 

[ajw22]

@onBalance any thoughts?

 

[cmdonnel]

Sorry, I couldnt post an EXCEL file, but here's the running log of my water test results since the last polish. Note - I excluded the Chlorine readings since I didn't think they were relevant here, but they were pretty consistent around 3-4:

Date	pH	TA	CH	CYA	Salt	Temp (F)
5/19/2024	7.6	110	110	0	0	62	(tank fill)
5/24/2024​	7.8​	90​	200​	0​	0​	65​
5/26/2024​	7.8​	90​	190​	20​	0​	65​
5/31/2024​	8​	90​	200​	20​	0​	68​
6/4/2024​	7.8​	90​	200​	30​	0​	68​
6/8/2024​	7.6​	70​	200​	30​	3000​	70​	(salt added, SWG turned on)
6/14/2024​	8​	110​	250​	30​	3000​	72​	(Sodium Bicarbonate added to raise TA)
6/23/2024​	8​	90​	250​	30​	3000​	75​
7/10/2024​	7.6​	80​	250​	30​	3000​	85​
7/26/2024​	8​	70​	300​	30​	3000​	82​	(first 1/2 of Calcium added)
8/17/2024​	7.8​	70​	420​	30​	3000​	88​	(second 1/2 of calcium added to go along with rising pool temps)
9/7/2024​	7.6​	70​	420​	30​	3000​	80​
9/21/2024​	7.8​	70​	420​	30​	3000​	74​
10/12/2024​	7.8​	90​	420​	30​	3000​	72​	(Sodium Bicarbonate added to raise TA)
10/26/2024​	8​	90​	420​	30​	3000​	68​
Pool Closed November 4th
11/16/2024​	8​	90​	420​	30​	3000​	65​
11/23/2024​	8​	90​	420​	30​	3000​	60​
11/30/2024​	7.8​	90​	440​	30​	3000​	55​
12/7/2024​	7.8​	90​	440​	30​	3000​	48​
12/14/2024​	7.8​	90​	440​	30​	3000​	42​
12/23/2024​	7.8​	90​	440​	30​	3000​	41​	(first noticed calcium deposits forming)
1/5/2024​	7.8​	90​	440​	30​	3000​	38​

 

[JamesW]

Are you brushing the pool on a regular basis?

You should do a thorough brushing with a plastic bristle brush at least once per week.

 

[JamesW]

10/12/2024​

7.8​

90​

420​

30​

3000​

72​

(Sodium Bicarbonate added to raise TA)

Why did you raise the TA when it was at 90?