Winter CSI and Calcium Hardness: big number really right?

[generessler]

I keep reading that CH of 250 is about right. But using PoolMath with my situation in the winter:

pH 7.8
TA 60
CYA 65
Water 40F
Salt 3000

It takes CH of 650 for a CSI of -.30 . By summer water will be 85F+, and CSI will be +.13. I don't like the idea of being in plus territory with a SWG.

How do folks manage this annual fluctuation? CH of 650 seems awfully high. With the nominal recommended pH of 7.4 it would be worse!

I've never had problems with scaling - including SWG plates. The grout and plaster of my 16-year-old pool seem fine.

When we moved in 2.5 years ago, indeed CH was ~200, which is about the fill water level. I raised it to ~450 and kept it there. This just requires a tweak now and then for overflow losses.

But it's cold again and PoolMath is causing me concern.. Not sure where to go. Just stick with 450? Or go higher now and worry about scaling later?

 

[ajw22]

Ignore the CSI in the winter.

Keep your CSI in range about 9 months out of the year and your pool will be fine.

 

[generessler]

Ignore the CSI in the winter.

Keep your CSI in range about 9 months out of the year and your pool will be fine.

Thanks! That's what I was hoping the answer would be.

 

[MSchutzer]

Just let your PH drift up a few tenths in winter to compensate. PH changes are reflected one to one in CSI changes. There’s no problem in letting it drift up 8.2 and that will raise your CSI by +0.4 compared to a PH of 7.8

 

[Gary Davis]

I'm just musing here... as I just opened a similar thread, where I don't disagree with @MSchutzer that the pH drifting up will help, as chasing pH for no good reason isn't something I'd do (I only affect the pH when I'm adding acid to lower alkalinity).

Also I'm in partial agreement with @ajw22 that short periods of time won't matter all that much since an aggressive CSI takes time to pull the plaster out of the pool, but I would disagree otherwise with the "ignore the winter" advice since the winter is the main time that the CSI becomes aggressive in the first place (due, of course, to the temperature mostly).

As for @generessler's comment that "250 CH is about right", it's certainly "in range" for most scenarios, especially given the TA is 60 ppm, where I generally strive for a 1:3 or even 1:4 ratio of TA:CH, 1:3 being 60:180 and 1:4 being 60:240, so that number is 'about right' in my book.

Bear in mind there isn't a 'magic ratio'; it's just what seems to work out well for people, based on what I've read and my own experiences.

 

[generessler]

Thanks! Really appreciate the thoughts. But I'm still not getting how 250 makes much sense if you're managing by CSI.

Typical recommended numbers with no SWG that I see scattered around in various sources:

pH 7.4
TA 100
CH 250
CYA 40

At water temperature 40F, CSI is -.51, well below the recommended limit of -.3. At 80F it's -.13, which is good but still quite negative. It hits the minimum at 60F: not very cold for most areas of the country. Yet I never see anyone recommending higher CH during colder weather.

My own status update: I am letting my pH drift up as dicussed here. Right now my actual numbers are

pH 8.0
TA 60
CH 430
CYA 70
Salt 2900

With current temp 35F (which of course _is_ very cold for NC), this is _still_ too negative at -.35. At a more normal 40 it will be at the limit. So I guess my plan is to make pH=8.0 my target for winter from here on. I think it tops out at about 8.1, so I'll let it do that.

Now if we can just get through the next couple of days with no burst pipes

 

[ajw22]

At water temperature 40F, CSI is -.51, well below the recommended limit of -.3. At 80F it's -.13, which is good but still quite negative. It hits the minimum at 60F: not very cold for most areas of the country. Yet I never see anyone recommending higher CH during colder weather.

CSI of +0.3 to -0.3 is ideal.

CSI of +0.6 to -0.6 is acceptable.

CSI falling to -.51 is fine during a few winter months. You are creating more work then necessary to manage the CSI in a very tight range.

 

[DanF]

Also, with your fill water's CH of 200 ppm, your pool's CH will continue to rise naturally. Wouldn't be surprised if it hit 500 (from 430) this summer.

 

[Gary Davis]

It hits the minimum at 60F: not very cold for most areas of the country. Yet I never see anyone recommending higher CH during colder weather.

I actually recommend doing just that so you've seen it, but maybe you've only seen it once.

• I'm doing ok... but I could be doing better (in terms of managing my CSI between summer & winter); how about you?

Most people in that thread, all of whom are kindly trying to help out, recommended against it though.

Also, with your fill water's CH of 200 ppm, your pool's CH will continue to rise naturally. Wouldn't be surprised if it hit 500 (from 430) this summer.

I've come to the belated conclusion we can't just look at fill water CH:TA, but also we have to look at rain water CH:TA (which is zero:zero, plus some acidity).

In the summer, under California conditions for example, there is nary a drop of rain so it's all fill water CH:TA changing the CSI (along with the other factors); but in winter, depending on whether we have a monsoon or not, the rain can add two feet of zero CH and zero TA fill to the pool (if we let it).

Each region though will have DIFFERENT fill water to rain water seasonal ratios but my point is that the fill water is drastically different depending on the season.

 

[generessler]

CSI of +0.3 to -0.3 is ideal.

CSI of +0.6 to -0.6 is acceptable.

CSI falling to -.51 is fine during a few winter months. You are creating more work then necessary to manage the CSI in a very tight range.

Thanks! But actually I'm trying to do the opposite: find one good CH number that will work all year. So maybe once or twice a year I can add a few pounds of calcium chloride to account for rain+overflow by bumping back up. (Our fill water is soft.)

I'm just saying that the typically recommended 250 doesn't make sense for that one number.

 

[Bperry]

Thanks! But actually I'm trying to do the opposite: find one good CH number that will work all year. So maybe once or twice a year I can add a few pounds of calcium chloride to account for rain+overflow by bumping back up. (Our fill water is soft.)

I'm just saying that the typically recommended 250 doesn't make sense for that one number.

Just raise your pH in the winter and the problem is solved. (But it’s really not a problem)

 

[Gary Davis]

I'm trying to do the opposite: find one good CH number that will work all year.

I think we ALL are perennially attempting to do that - although I can't speak for anyone else - so I'll agree that I am trying to find that magic set of numbers too.
a. Either a magic set of year-round numbers to aim for exists (given our individual fill-water situations),
b. Or a set of year-round magic numbers do not exist (and then we have to accept the least egregious workaround)

Many people say the magic numbers don't exist - so you have to either live with too much CH in the summer or too little in the winter (or you adjust it accordingly).
Luckily, the need for fill water (or the inevitable dilution from rain) causes you to re-adjust anyway since the numbers aren't static over those conditions.

As I understand it, these 3 of 7 saturation factors are (almost) completely out of your control:

• Temperature
• TDS/Salt (within reason)
• CYA (within reason)

And these 2 of 7 saturation factors are only somewhat under your control:

• pH (equilibrium, it will inevitably trend toward the floor/ceiling, which will depend a lot on Boron/TA)
• TA (carbonate alkalinity)

And these 2 of 7 saturation factors are (almost) totally under your control:

• CH
• Borate (I only add this to be complete, but the OP isn't using borates, AFAIK)

Please correct me if I'm wrong.
If I'm right, then it tells you which factors you can control year round, and which you can't really control all that well.

I'm just saying that the typically recommended 250 doesn't make sense for that one number.

Sticking to a single number (outside the other numbers) is fraught with difficulty.

It's my understanding, for example, that you can achieve the same saturation index with high alkalinity & low calcium as you could with low alkalinity and high calcium - but - and this is the biggie - but - with high alkalinity you'll have OTHER problems (such as controlling the pH rise) more so than you would have with high calcium.

It's not easy and it may even be impossible to find a single set of magic year-round numbers that keep the saturation index where you want it.
(Certainly I haven't found those magic numbers yet - and even if I did - they don't survive contact with the inevitable enemy of rain and evaporation.)

With all that in mind...
What I strive for, is a (roughly) 1:3 or 1:4 ratio of TA (carbonate alkalinity) and CH (Snow Joe) of around 100:300 in the summer & 100:400 in the winter (all the while keeping the saturation index as close to 0 as I can [knowing the other key factors play a role... some of which are completely out of my control]).