# Does the Calculator Properly Calculate Si?

#### Sammy2

##### Well-known member
Using the temperature adjusted Si formula, Si = pH + Ti + Ci + Ai - 12.1, I get numbers different than the calculator gets so I'm wondering if it is properly calculating it. I know I want to get that number as close to 0.00 as I can so should I use the formula or the calculator?

TIA

#### pooldv

TFP Expert
Platinum Supporter
I thought you had an SWG, if yes then you want -0.3 to 0. And since you are in CA and probably have water that tends to scale you probably want -0.3 to 0 anyway.

Yes, the PoolMath CSI calculation has been discussed and analyzed to the Nth degree in lots of threads by all manner of scientists, chemists and lab rats. Do some searches in the top right corner and read as much of that as you are interested in reading.

For me, I'll say the calculation works just fine in my pool. I've kept my CSI between -0.3 and 0 for 5 years and I've had no scale and my SWG has never needed cleaning. When it drifted up above 0 for a bit I had a slight build up on the tile at the water line. As soon as I moved it back below 0 it disappeared and hasn't been back in a couple of years. So, the CSI calculation looks perfect to me.

#### Patrick_B

TFP Expert
Use the calculator.

If you have the overall parameters near correct in the pool, it's rare you need to worry about the saturation index. Most of the time, it can be ignored in most pools. Almost always.

#### mas985

TFP Expert
Using the temperature adjusted Si formula, Si = pH + Ti + Ci + Ai - 12.1, I get numbers different than the calculator gets so I'm wondering if it is properly calculating it. I know I want to get that number as close to 0.00 as I can so should I use the formula or the calculator?
Which "SI" index are you using? The calculator uses CSI which is not the same as LSI.

But to get to zero simply change PH by the opposite of the index since they are directly related.

OP
OP

#### Sammy2

##### Well-known member
I do have a SWG, guess I need to modify my signature!

So is the calculator using the formula posted here and not the one that his in the Hayward manual? I suppose if it does it is more accurate and then I can keep it in the range that will clean up my scaling, hopefully since my CH is 600ppm, which is too high.

I'd really like to find out where all the constants came from in the formula set, as well as the development of the formulas themselves but I suppose that's just the engineer in me.

TFP Expert