Pebblecrete and Calcium Hardness

[AlexHush]

Hi all,

I would like your opinion please on what is the highest Calcium Hardness level I can have in my pebblecrete pool?

I have seen a lot of conflicting information which makes things all the more confusing.

The TFP PoolMath Calculator says for SWG and Plaster pool surface (not pebblecrete specifically) the Ideal CH is 350 to 550 and Acceptable CH is 250 to 650.

Do pool chemistry recommendations change with pebblecrete as opposed to plaster? The PoolMath Calculator doesn't have a pebblecrete option.

Pool articles on the internet that talk specifically about pebblecrete say a CH range between 200-400.
My local pool shop says maximum CH of 300.

I know that having a higher CH helps to have more balanced water according to CSI which is why I was thinking of increasing it as much as safely possible.

My pool water chemistry at the moment is:
FC 5
pH 7.7
TA 70
CH 400
CYA 70
Salt 4400 (400 higher than the recommended for my SWG)
Temp 27 Celsius
CSI -0.17

Any insight, suggestions and recommendations on my pool chemistry would be great.

 

[ajw22]

Your CH and CSI are fine. Do not increase your CH. More CH will not improve anything.

 

[mgtfp]

Pool articles on the internet that talk specifically about pebblecrete say a CH range between 200-400.
My local pool shop says maximum CH of 300.

The 300 max makes sense from a pool store perspective that would recommend higher TA to be maintained (which doesn't make sense, on the other hand). With your TA of 70, you are fine with CH 400. No need to increase it further, but also no need to force it down. What matters is the CSI, and that is fine.

 

[JoyfulNoise]

Let me ask you this - do you care more about the absolutely imperceptible and minor degradation of your pebblecrete finish that might happen (or might not) due to lower CH levels, OR, do you care about not wrecking and destroying your $1000+ chlorine generator in order to maintain higher CH levels in line with “industry standards” ?

(It’s not a false-choice)

As others have stated, your chemistry is fine. Most of the recommendations regarding plaster exist to give liability cover to the manufacturers and applicators and have no real-world, scientific validation behind them. They exist in isolation as if the only thing that matters to a pool is the surface finish. If that were true, then one would never chlorinate pool water as the presence of chlorine and the resulting chloride load leads to more damage and loss of color than anything CH will affect.

 

[AlexHush]

Let me ask you this - do you care more about the absolutely imperceptible and minor degradation of your pebblecrete finish that might happen (or might not) due to lower CH levels, OR, do you care about not wrecking and destroying your $1000+ chlorine generator in order to maintain higher CH levels in line with “industry standards” ?

(It’s not a false-choice)

As others have stated, your chemistry is fine. Most of the recommendations regarding plaster exist to give liability cover to the manufacturers and applicators and have no real-world, scientific validation behind them. They exist in isolation as if the only thing that matters to a pool is the surface finish. If that were true, then one would never chlorinate pool water as the presence of chlorine and the resulting chloride load leads to more damage and loss of color than anything CH will affect.

Yes I understand, I'd rather protect the chlorine generator. May I ask what CH level would you aim for in this case for the long term?

Thank you

 

[JoyfulNoise]

If it were my pool, I would always aim for the lowest CH in the range that allows my pool water to equilibrate to a higher pH and TA while still maintaining a zero or slightly negative CSI.

For example, my fill water has a CH of 200ppm, a TA of 120ppm and a pH that ranges from 7.6 to 7.8. Pools will always concentrate CH a bit unless you get good rainfall or use a water softener. In my case I have a water softener so my goal is to get and keep my pool water CH around 250ppm and then let my TA and pH come close to their more natural values. Doing this would reduce acid addition greatly as the water would hover at a pH of around 7.8 to 8.0 while still maintaining a proper CSI. This would also put a much lower burden on my SWG in terms of calcium scaling.

 

[AlexHush]

Great info, thanks very much for this.