White Powder, High CH but CSI Ok?

[PoolFlunkie]

CH=550
TA=50
pH=7.4
CYA=70
Salt=3500
Borate=50
TC=3.0
FC=3.0
Temp=80
CSI=-0.05 per Taylor Watergram
CSI=-0.59 per TPF Calulator

Up until about a year ago my pool ran at a ph > 7.8. The white plaster had a general greyish stain. A year ago I treated with the pink Scale-Tec liquid and began running my ph around 7.2-7.4. The stain slowly went away and the plaster looks good now. Pool is crystal clear. Since then I have had a fine white powder in my cleaner bag. It appears to be calcium carbonate since it fizzes vigorously with muriatic and fizzes pretty good with vinegar. Do I need to be concerned about high CH if the CSI is Ok? Is the white powder coming from the stain being removed or from the plaster itself? Do the Taylor and TPF CSI values usually not coincide? Thanks!

 

[JoyfulNoise]

The Scale-Tec is sequestering the calcium ions in the water. It will also interfere with your CH test in that it will likely make the apparent CH lower than what it is. As the scale-tec breaks down from chlorine exposure, it liberates calcium ions which likely precipitate as calcium carbonate. So between the calcium scale stain and your plaster, the calcium is just coming out of solution.

Your water is way too aggressive at nearly -0.6 CSI. You should target a CSI between 0 and -0.3 to keep your plaster happy. Otherwise you're just removing calcium from the plaster, sequestering it with the scale-tec and then dropping it out of solution.

 

[needsajet]

Welcome to TFP! Good to have you here

The Taylor calculator is a different index known as the Langelier saturation index modified for pools or LSI. The CSI used here at TFP is the calcite saturation index.

 

[PoolFlunkie]

Thanks very much for the responses. Using the Pool Calculator, if I raise the TA to 70 and pH to 7.6, the CSI goes to -0.17. Do I need to change out any water to lower the CH or can I run it where it is? In other words can I only concern myself with getting the CSI between 0 and -0.3?

 

[needsajet]

You can leave your CH where it is, and yep, your plan is sound.

The only tweak worth mentioning is to try a smaller increase on TA to 60 instead of 70, and see if pH will settle around 7.8.

 

[PoolFlunkie]

Thanks! Out of curiosity, why would you shoot for 60 TA and 7.8 pH vs 70/7.6?

 

[pooldv]

Because you likely cannot achieve TA of 70 and pH of 7.6 without having to regularly add acid to lower PH and baking soda to raise TA. With TA at 60, or maybe 50, it is possible that your pH and TA will remain stable with little or no additions of acid or baking soda.

 

[PoolFlunkie]

Got it. Thanks for the help!

 

[PoolFlunkie]

Pool looks great. The amount of white powder has significantly decreased. pH has been 7.8 to 8; TA 60-70, CH=550, CYA=65, salt=3500; borate=50; temp = 70. I get a CSI of 0.0 to -0.1. Seems good to me. This is so different from the pool store recommendations that I wanted to check in again on it. Specifically, 550 CH along with the other readings should be ok? thanks!

 

[needsajet]

Great work on your pool water chemistry!

Yes, all is fine. When the pH rises above 7.8, drop it to 7.6 or 7.7 (probably what you've been doing?)

You've got a bit of room to run on your CH. Somewhere up around CH of 850 and as the water warms up, your CSI will get a bit higher than ideal. You can then run your pH a little lower to compensate. Or, if you find that you're adding acid more often than is convenient for you, then you would consider a water exchange. Do you get a bit of rain in the next while? That might also reduce your CH if you're able to drain some water off.

I like the name of your suburb!

 

[miles267]

Great work on your pool water chemistry!

Yes, all is fine. When the pH rises above 7.8, drop it to 7.6 or 7.7 (probably what you've been doing?)

Saw your comment about pH. I've been deliberately targeting pH of 7.5 based on Pool Math. When it rises to 7.8, I jump to drop to 7.5. My TF-100 doesn't show 7.6-7.7.

Is pH of 7.5 ideal? Or 7.8?



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[Caco]

The ideal ph is a range of anywhere between 7.2-7.8
Normally ph rises quicker from 7.2-7.5 than from 7.5-7.8. That's one of the reasons we suggest dropping your ph to about 7.5, as going as low as 7.2 doesn't give you much additional time between doses

What Needsajet was referring to was the best ph range for your CSI value, in the green box near the bottom of the poolmath table. Your ph can have a big effect on maintaining your CSI to between -0.6 to 0.6. So pick a ph value within the range of 7.2-7.8 to best manage your CSI

 

[needsajet]

Anywhere from 7.5 up to 7.8 is clear sailing. I leave mine alone

Given the history of the pool, I'd run it within a tight range (-0.3 to 0.0) and then widen out gradually only if need be for convenience.

Agree with Caco that below 7.5 is inefficient.

So it sounds like you got the problem fixed. Way to go!!!