Where is this CH coming from?

[pinguy]

PH - 7.5
TA - 60
CYA - 50
FC - 6
CC - 0
CH - 475

I have no idea why my CH is so high. This is our first season, and we started out with a CH of around 150.

We have nasty well water, but got water trucked in to fill the pool originally - and only added about 20 lbs of calcium flakes to that. We haven't had to fill much at all from the hose. But to be sure I tested the hose water, and the CH is only 100.

Why is this happening? I haven't used any Cal-Hypo. We have a natural rock feature, can calcium be leeched from the rocks?

I starting to notice white deposits on the hydraulic cement around the rocks and maybe a little around the tiles.

 

[JoyfulNoise]

What are rocks composed of? How much of the waterfall water is exposed to the hydraulic cement? Any estimate of how much fill water you have added?


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[pinguy]

What are rocks composed of? How much of the waterfall water is exposed to the hydraulic cement? Any estimate of how much fill water you have added?

Not sure what rocks are made of, or how to quantify your second question. I've attached pictures. Probably about 4 inches of fill water from the hose this season.

 

[smackdab]

If you started with a CH of 150 and your fill water is 100 CH, then about 90,000 gallons of fill water would have to be added because of evaporation to reach a CH of 475 so you know that didn't happen. Or in order for your CH to jump from 150 to 475 with 4" of fill water, the fill waters CH would have to have been 7,800 ppm. This basically eliminates your fill water. It would have to have come from the pool surface or the rocks or you possibly didn't start out with CH 150 ppm.

 

[JoyfulNoise]

Wait, this is a plaster pool...I always think East Coast pools are all vinyl lined (what can I say, I'm biased).

Duh (to me) - the CH came from the giant source of calcium in your pool, ie, the plaster curing process. Plaster surfaces emit some calcium during the curing process. When an acid start process is used (fairly common), the CH increases because the acid neutralizes the calcium oxide in the plaster which eventually converts to calcium carbonate in the pool water. That's why TFP recommends the bicarbonate start up, it emits the least amount of calcium into the water. Unfortunately most plasterers don't subscribe to it so you're stuck with the excess CH.

The white stuff on the edges of the cement/rocks is efflorescence and calcium scale. You can scrub it off with some dilute muriatic acid.


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[pinguy]

Wait, this is a plaster pool...I always think East Coast pools are all vinyl lined (what can I say, I'm biased).

Duh (to me) - the CH came from the giant source of calcium in your pool, ie, the plaster curing process. Plaster surfaces emit some calcium during the curing process. When an acid start process is used (fairly common), the CH increases because the acid neutralizes the calcium oxide in the plaster which eventually converts to calcium carbonate in the pool water. That's why TFP recommends the bicarbonate start up, it emits the least amount of calcium into the water. Unfortunately most plasterers don't subscribe to it so you're stuck with the excess CH.

The white stuff on the edges of the cement/rocks is efflorescence and calcium scale. You can scrub it off with some dilute muriatic acid.


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Thanks! So where does that leave me? The PH is definitely going to go above 8 in the winter, am I risking scaling? I feel like if it was a problem the PB would have said something

 

[JoyfulNoise]

Thanks! So where does that leave me? The PH is definitely going to go above 8 in the winter, am I risking scaling? I feel like if it was a problem the PB would have said something

I assume you'll be closing and covering the pool, correct?

Look at PoolMath and put your numbers in -

Temperature...............CSI

80F......................-0.09
70F......................-0.18
60F......................-0.28
50F......................-0.37
32F......................-0.55

And, if your pH goes up to 8 and you assume Temp = 40F, then your CSI = -0.01.

Calcium carbonate has retrograde solubility which means that it becomes more soluble in water as the temperature goes down. Therefore you need to manage your pool water until the temperatures go below 60F (maybe even wait until 50F) BEFORE you close your pool. If you want to give yourself more of a buffer, try to lower your TA to 50ppm and get your pH down to 7.5 at closing. Since the water will be cold, you can expect the pH rise and other chemical reactions to greatly slow down. I think your pool water will be fine and scaling should not be an issue.

When you open back up in the spring, you'll be adding a lot more fresh water back into the pool. Even with your well fill water at 100ppm CH, that is lower than your pool water so you will dilute your opening CH value a bit.

 

[pinguy]

I assume you'll be closing and covering the pool, correct?

Look at PoolMath and put your numbers in -

Temperature...............CSI

80F......................-0.09
70F......................-0.18
60F......................-0.28
50F......................-0.37
32F......................-0.55

And, if your pH goes up to 8 and you assume Temp = 40F, then your CSI = -0.01.

Calcium carbonate has retrograde solubility which means that it becomes more soluble in water as the temperature goes down. Therefore you need to manage your pool water until the temperatures go below 60F (maybe even wait until 50F) BEFORE you close your pool. If you want to give yourself more of a buffer, try to lower your TA to 50ppm and get your pH down to 7.5 at closing. Since the water will be cold, you can expect the pH rise and other chemical reactions to greatly slow down. I think your pool water will be fine and scaling should not be an issue.

When you open back up in the spring, you'll be adding a lot more fresh water back into the pool. Even with your well fill water at 100ppm CH, that is lower than your pool water so you will dilute your opening CH value a bit.

Thanks as always. I was wondering when that CSI part of pool math would become useful :-D