1. ## LSI vs Poolmath

my chemistry numbers are:
FC 6.0
pH 7.7
TA 90
CH 250
CYA 30
water temp 46°
no borates.

using PoolMath the saturation index is -0.18. using the Langelier formula the saturation index is approximately -0.05. i calculated LSI using Taylor's Water Balance Calculator wheel that came with my K-2006 test kit.

why is PoolMath's saturation index so different from LSI's?

2. ## Re: why are PoolMath and Langelier saturation index numbers different?

This is kinda confusing for me, but there are a couple threads here

http://www.troublefreepool.com/archive/index.php/t-75058.html

3. ## Re: why are PoolMath and Langelier saturation index numbers different?

Put very simply, they are two different formulas. PoolMath uses the CSI....

http://www.aquaticsintl.com/water-qu...-real-csi.aspx

I fear this is headed into "The Deep End."

4. ## Re: why are PoolMath and Langelier saturation index numbers different?

Do you have the water temp factored in both?

More here, Langelier and Calcite Saturation Indices (LSI and CSI)

5. ## Re: why are PoolMath and Langelier saturation index numbers different?

Read the links posted above for the detailed discussion. Essentially the pool industry modified the original LSI factor to try to make it work for pool water but it, the LSI, was never intended for open water systems like pools. The CSI was developed to specifically address open water bodies (like pools and spas) and comes much closer to actually predicting scale and corrosion than the LSI does.

Also, remember that these indices simply give you a measure of how over-saturated or under-saturated your pool water is with respect to calcium carbonate concentration. The CSI will tell you if you are in an unbalanced state but it tells you nothing about the rate of plaster corrosion or the speed of scale formation.

6. ## Re: LSI vs Poolmath

Marcion333,

This is of little interest to almost everyone on this forum. Appropriately, I have moved it to the deep end.

7. ## Re: LSI vs Poolmath

Also Marcion, in many cases your CSI will be fine with the specific guidelines we suggest using. There are Caveats as with most things, but that's generally true. As said, LSI is more useful for other applications, and we use it extensively in my industry. CSI is also used and we rely on both for making lots of important and often critical decisions. CSI works well for pools since CaCo3 is by far our greatest concern. Typically, the other constituents don't reach levels of concern in most pools most of the time, but it's interesting stuff if you like delving into such things.

8. ## Re: LSI vs Poolmath

As indicated above, while the CSI may be a more recent upgrade, there is not a lot of difference between the LSI and CSI, as both are calculated similarly. Neither Index is absolute on predicting what will happen in a plaster pool.
Also, in terms balancing pool water, there is not a lot of difference between a -0.05 and -0.18. Both numbers are well within the "balanced" range.
Both formulas provide a good idea of whether the pool water is within the balanced range or not.

9. ## Re: LSI vs Poolmath

i thank everyone who appreciated my interest in trying to understand this issue and replied, and also thanks for the links.
as cody in the Dual Survival series said, "Knowledge is power, and its very lightweight."

10. ## Re: LSI vs Poolmath

No problem, that's what we come here for, so it's good to hear you're enjoying the forum.

11. ## Re: LSI vs Poolmath

LOL! Knowledge is lightweight. Never heard that before, I like it.

12. ## Re: LSI vs Poolmath

Originally Posted by pooldv
LOL! Knowledge is lightweight. Never heard that before, I like it.
Ours especially!

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