Poolmath goals

[Foonly]

I have been playing with the various goal ranges suggested by the Poolmath web page and comparing its suggestions with what it says in my SWG manual. I am wondering about the difference between the "Traditional Pool" and "Troublefree Pool" settings. The "Traditional" goals pretty match what is in the SWG manual while the TFP goals tend to be a little higher and a little tighter. Is there an explanation somewhere about how these numbers were arrived at?

For example, the SWG manual says CH between 200 and 400, but Poolmath says 350 to 450. Raising my pool from its current 240 to 350 requires 10 pounds of Calcium Chloride. I want to know why this difference.

 

[Texas Splash]

For example, the SWG manual says CH between 200 and 400, but Poolmath says 350 to 450. Raising my pool from its current 240 to 350 requires 10 pounds of Calcium Chloride. I want to know why this difference.

Interesting you bring this up. Here at TFP, our experts have compiled data from thousands of pools, types, and geographical areas to develop what has become our Recommended Levels (by type). Many in the pool industry (manufactures, builders, installers, etc) continue to utilize very basic, almost outdated levels across the board.

For the CH specifically, there was a concern in the past about water becoming too aggresive for SWG pools because our recommended levels listed a higher CYA along with a slightly lower TA and pH. So the slightly higher CH (minimum) seemed to compensate for the others being a bit lower which could impact a pool's CSI - especially in the winter when CSI levels tend to plummet. But recently there have been discussions at TFP about modifying the lower-end of the CH scale since for the most part, most users are more concerned with the devlopment of scale. Most owners are very apprehensive about adding calcium, especially in areas that alreay have hard water.

All of this to say that if your CH is currently at 240, I would not rush to raise it. Instead, enter all of your pool levels into the PoolMath tool and refer to the CSI row near the bottom. A slightly negative CSI from zero to -0.3 is acceptable. If it was to dip much lower, simply allow your pH to rise a bit to compensate and you'll be fine. As water temps increase and/or refills add more CH to the water, your CH should be just fine. Hope that helps.

 

[Foonly]

Interesting about CSI. Poolmath gives me -0.3 (that's bad by their rules, ok by TFP) but following the formula in the SWG manual I get +0.06 (that's good). Their formula for "Saturation Index" is Si=pH+Ti+Ci+Ai - 12.1. Those 'i' values come from looking up temp, CH, and TA in a little table. They say the Si should be ± 0.2. Maybe the tables are different too? I can't see the one TFP uses but here is the one from the Hayward manual.

My values are ph=7.4 TA=100 CH=240 Temp=88

 

[jblizzle]

We trust PoolMath, does not matter what their table says

There is a higher likelihood of scale forming in the cell if the CSI is positive. Leading to acid cleaning. Leading to shorter cell life. Thus the suggestion to keep it slightly negative.

 

[Richard320]

Interesting about CSI. Poolmath gives me -0.3 (that's bad by their rules, ok by TFP) but following the formula in the SWG manual I get +0.06 (that's good). Their formula for "Saturation Index" is Si=pH+Ti+Ci+Ai - 12.1. Those 'i' values come from looking up temp, CH, and TA in a little table. They say the Si should be ± 0.2. Maybe the tables are different too? I can't see the one TFP uses but here is the one from the Hayward manual.
View attachment 103495
My values are ph=7.4 TA=100 CH=240 Temp=88

Theirs is probably the Langelier Saturation Index, which was developed to combat scale in boilers. Your water doesn't get that hot, so it's not as useful. The amount of salt in the water also affects how aggressive the water is to concrete. They seem to ignore that.

 

[Foonly]

My intent is to follow the TFP guidance. But replacing or cleaning a SWG cell is a lot cheaper than replastering the pool! Doesn't overly negative CSI eat at the walls?

 

[Richard320]

My intent is to follow the TFP guidance. But replacing or cleaning a SWG cell is a lot cheaper than replastering the pool! Doesn't overly negative CSI eat at the walls?

Yes. But that doesn't usually happen until it sits at -.6 for a while.

Your pH is going to rise naturally, and the water may warm up more, and with evaporation and refills, the CH will climb. All these will push CSI positive.

If you're that interested in the topic, use the search box. There have been lengthy threads discussing this stuff. Look for any of the older ones written by chemgeek

 

[Foonly]

Just got new Hayward "SwimPure Extreme" 40,000 Gallon SWG installed and the manual has updated that CSI chart again. Instead of subtracting a fixed 12.1 there is a new term based on "Total Dissolved Solids". From my research here, this is largely a useless measurement, so I will just go with what PoolMath tells me.

One interesting tidbit I picked up from the installer that is not in the installation manual: current guidance is that with variable speed pumps the cell needs to be installed upside down. Apparently at low flow rates all of the plates do not get covered due to the offset nature of the Hayward cells. Well maybe, if there was air in the lines. Anyway, that's how he installed it. The slowest my pump will go is 20 GPM.

 

[jblizzle]

Yup, I have mine upside down too.