CSI (Calcite Saturation Index)

[Catanzaro]

I am trying to grasp this concept, but having a tough time with the "Less than" and "Greater than" part.

-0.6 until 0.6 (Is this good)? Thank you.

Calcite Saturation Index - requires pH, TA, CH, CYA, Temp, uses Borate, Salt
Less than -0.6 is suggestive of problems for plaster, tile, stone, and pebble pools.
Greater than 0.6 is suggestive of problems for all pools.

 

[JoyfulNoise]

Those are the extremes. The scale is logarithmic which means that there's twice as much calcium saturation at +0.6 as there is at +0.3. Some other things to keep in mind is that pools don't typically see scaling until you get beyond +0.6, so scaling is very likely at +0.7 and almost definite if you hit +1.0. For spas with lots of aeration and high temperatures, scaling can be see at +0.3 in some cases.

On the negative side, being between 0 and -0.3 is fine and even going to -0.6 is ok for a short period of time. However, extended periods of time with the water at or below -0.6 can lead to plaster damage (etching).

Your pool is vinyl, so a negative CSI is really not an issue (although highly negative CSI means your water balance is probably not in a "happy" place). Positive CSI values are worse for vinyl because you can get scaling which will lead to a rough feel to your liner. SO for you, I'd say try to keep your CSI between -0.2 and +0.2 and don't really worry too much if you're negative.

 

[Catanzaro]

On the negative, anything past -0.7 until -1.0 (for example) is bad and on the positive side anything past 0.7 until 1.0 (for example) is bad.

Just want to make sure I am understanding this. A lot of forum posts have plaster pools. Even though I help, sometime I get caught up in CSI, which I believe is more important than vinyl pools (which I always understood). My CSI always seems to be -0.03, which almost seems to be perfect. It is only when the water temperature drops to about 30*, which is for a very short time, my CSI change is -0.51, which is not a big deal.

I was having trouble interpreting the negative side, not the positive side. In reality, the negative becomes greater, not necessarily less. Less than is really greater than (if this makes sense).

 

[JoyfulNoise]

For vinyl pools, negative CSI is not a big deal. Vinyl damage is typically driven by excessively low pH AND high FC such that the hypochlorous acid oxidizes the liner (bleaches out the colors) and the low pH weakens the vinyl causing embrittlement and cracking. Very high pH can cause vinyl to swell but both of those extremes would be hard to get to without the pool owner noticing something is wrong with the water.

Remember, CSI is the degree to which the water is saturated with calcium carbonate (can absorb or emit calcium carbonate). 0 means the water is perfectly saturated, negative is under-saturated and positive is over-saturated. It's a representation of the thermodynamic driving force for calcium movement but says nothing about rate or initiation of the movement process.


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[Catanzaro]

Remember, CSI is the degree to which the water is saturated with calcium carbonate (can absorb or emit calcium carbonate). 0 means the water is perfectly saturated, negative is under-saturated and positive is over-saturated. It's a representation of the thermodynamic driving force for calcium movement but says nothing about rate or initiation of the movement process

Thank you. Now this makes more sense.

 

[BuckeyeChris]

-1 is less than -.5, so I believe the wording is accurate.