Conflicting CSI values: Taylor Watergram vs PoolMath

[aggiejet]

When I enter the results of testing of my water, the Taylor supplied Watergram whiz wheel gives a different answer that the results obtained on PoolMath.

Today's readings:
TA: 110
CH: 220
Ph: 7.6
Temp: 88

Watergram: .15
PoolMath: .04

The Watergram is educational because it demonstrates how all of the variables can affect your CSI. But I love the ease of PoolMath. Just curious about the different values.

Thanks

 

[JamesW]

For the watergram, you have to use adjusted TA, which subtracts the CYA contribution to the TA.

Try subtracting 1/3 of CYA from the TA.

 

[aggiejet]

That pretty much squares it up. Thanks!

 

[JamesW]

 

[JamesW]

For the watergram, you have to use adjusted TA, which subtracts the CYA contribution to the TA.

Try subtracting 1/3 of CYA from the TA.

Note that the actual percentage of the cya depends on the pH.

pH......%CYA to subtract from TA.

7.0.....0.22CYA.
7.2.....0.26CYA.
7.4.....0.30CYA.
7.6.....0.33CYA.
7.8.....0.35CYA.
8.0.....0.36CYA.