Pool Math CSI vs Taylor Watergram

[Mr. Muriaticacid]

I have been using the Taylor Watergram calculator for about 4 years. I like the convenience of the Watergram. I have seen the Pool Math calculator and have sort of played with it a little but it wasn't until today that I noticed a difference between the two calculators. Is it me or is there a real difference?

Here is my example:

POOL MATH

FC 6.0
CC 0.0
pH 7.3
TA 60
CH 550
CYA 50
BORATES 50ppm
TEMP 80
CSI -0.48 (Corrosive)

Taylor Watergram

Same numbers as above:

CSI -0.05

Can someone check this and let me know if I am doing something wrong! Can there be this much of a difference? If this is the case, my numbers are out of whack and have been for years. This would explain the episodes of scale and pitting in the plaster. I can't believe the huge difference between the calculators.

I would like to figure this out before I close in a few weeks so I don't open up to any more surprises.

Also, I have never checked my water after closing the pool, should I? I figured there was no way to circulate the chemicals so why bother with it. What do you all do?

 

[JamesW]

Using the Watergram, you can't use total alkalinity, you have to use carbonate alkalinity, which is total alkalinity minus cyanurate alkalinity and borate alkalinity.

You also have to put in a correction for salinity with the Watergram.

 

[JamesW]

To calculate the cyanurate alkalinity or borate alkalinity.

Acid/base = 10^(pka - ph)
10^(6.88-7.3)=0.38.
1÷1.38=72.5% cyanurate.
.725 x 50 ÷ 129.074 x 100.09 ÷2 = 14

10^(9-7.3)= 50.12.
1÷51.12= 1.956% borate.
0.01956 x 50 ÷10.81 x 100.09 ÷2 = 4.5 ppm borate alkalinity.

So, you subtract 14 ppm from the TA for the cyanurate alkalinity and 4.5 ppm from the TA for the borate alkalinity.

You would use 41.5 for the alkalinity when using the Watergram.

 

[Mr. Muriaticacid]

To calculate the cyanurate alkalinity or borate alkalinity.

Acid/base = 10^(pka - ph)
10^(6.88-7.3)=0.38.
1÷1.38=72.5% cyanurate.
.725 x 50 ÷ 129.074 x 100.09 ÷2 = 14

10^(9-7.3)= 50.12.
1÷51.12= 1.956% borate.
0.01956 x 50 ÷10.81 x 100.09 ÷2 = 4.5 ppm borate alkalinity.

So, you subtract 14 ppm from the TA for the cyanurate alkalinity and 4.5 ppm from the TA for the borate alkalinity.

You would use 41.5 for the alkalinity when using the Watergram.

Thank you James W. I thought I read on the forum to disregard using that conversion but they were probably talking about when using Pool Math and not the Watergram. Well, that explains it. I am at work right now so I don’t have access to my Watergram but I’ll bet that using that by using that conversion the numbers will be similar. I’ll be using Pool Math exclusively in the future. Thanks again.

 

[JamesW]

If you have a salt pool, you also subtract 0.25 from the CSI as a TDS correction when using the Watergram.

 

[JamesW]

Using 41.5 for TA and using the TDS correction, the Watergram and PoolMath agree.

 

[peirek]

What is your Salt level? You will need your Salt reading to complete the full analysis of your CSI using PoolMath. Using 3000ppm I get CSI = -0.43. You certainly can let your pH drift up to 7.8 to get your CSI nearer to 0 (-0.05).