Adjust the Calcium Hardness for a vinyl pool with a SWG?

[imalittleturt]

I have an above ground pool with an aquatrol SWG. The manual states to keep Calcium Hardness at 200-400. I have a vinyl pool and I remember reading that you do not need to adjust the CH for a vinyl pool. Should I just leave the level alone or is it best for the SWG to get the CH with in range. My current value is 70 ppm. Thanks.

 

[Poolsean]

In a vinyl liner pool, the calcium hardness is not that important. However, I would recommend that you have the water tested and compared to the saturation index, which determines if the overall water chemistry is balanced, corrosive, or scale forming. It is the last condition that can cause problems with the swg.

The good thing is that once you've balanced your water to the saturation index, the swg should not do anything to cause it to come out of balance and should ensure proper operation of your salt system.

So, having said that, if you can provide a complete water chemistry test, we can help determine if you're balanced, or what chems are needed to balance your pool.

Free Chlorine
Total Chlorine
pH
Total Alkalinity
Calcium Hardness
Water Temperature
Cyanuric Acid
Salinity.

 

[Guest]

I

The good thing is that once you've balanced your water to the saturation index, the swg should not do anything to cause it to come out of balance and should ensure proper operation of your salt system.

thst is assuming the ph doesn't change but SWGs do cause a pH rise because of the aeration effect of the hydrogen gas generated along with the chloirne.. pH rise is the MAIN factor that will predict scaling so once your water is balanced monitor your pH and make sure it does not rise above about 7.8 at any time.

 

[Poolsean]

But even with a low calcium hardness level, you can afford to drift up in pH and not have scale, right?

I didn't mean to imply that the pH will not shift, and I agree, you still need to test and maintain your pH.

 

[Guest]

But even with a low calcium hardness level, you can afford to drift up in pH and not have scale, right?

I didn't mean to imply that the pH will not shift, and I agree, you still need to test and maintain your pH.

If you look at the math used to calculate the SI pH is the ONLY factor that is a direct one. The CH and TA are log base10 of the ppm reading which means it takes a VERY BIG change in either TA or CH to create scaling conditions but a very small upward change in pH can take balanced water and make it have a tendency to scale. As we both know, SWGs have a negative impact on pH since they create conditions that promote the rise in pH and, consequently, scaling conditions, even when the CH is not that high.
So, to answer your question, no--even with lower calcium levels high pH will create a scaling condition if the pH rises enough (and I have seen enough salt pools with pH so high it was not even able to make an acid demand test change the color of the indicator after 10 drops!)
Scaling of the cell has a direct impact on chlorine production, as you well know!

 

[imalittleturt]

Here are my test numbers from last night. I am using the Taylor K-2006. I just added CYA 3 nights ago so I am wating till the weekend to test for its value. This is a new pool, it has been filled for about 5 days now, 3 of which it has rained. I am just trying to get the water balanced before I hook up the auqatrol. I will start adding the salt this week, hopefully tonight. Thanks.

FCL: 2.4
CC: 0
TC: 2.4
PH: 7.2
TA: 120
CH: 90
CYA: ? not know yet
Temp: 58F

 

[JasonLion]

Your numbers look fairly good. You will want CYA to end up between 60 and 80. You should also allow TA to fall naturally until it is in the 70 to 90 range. Once the water temperature comes up a bit the PH will tend to drift up, so keep an eye on it and don't let PH get above 7.8.

Your calcium is fine where it is because you have a vinyl pool. If you had a plaster pool you would need to bring CH up more to where they recommend in the manual.