Recommended levels

[The Mermaid Queen]

Ok, I will toss in my 2 cents on the pH and CH issues.

pH: I think the wider range of 7.2-7.8 is more practical for the average user, as long as that does not cause any damage. The benefits of a tighter range can be discussed elsewhere. I am pretty sure I have suggested 7.2-7.6 in the past. And now that i think about it, are most scales not in increments of 0.2 ppm? So to ask for 7.5 would just be a guess anyway. AND, don't we always say a lower pH allows the chlorine to be more effective? I think of 'low' as 7.2-7.4.....

Hey, the smilies are back!

CH: I was not aware that there was an actual minimum for vinyl (and I just barely remember it for FG now that you mention it.) Just not to let it get TOO high because of scaling issues. (I believe on PF it was stated not to worry unless it got over 400 or maybe even 500?) Now, there may have been other discussions that I just did not follow on the merits of SOME CH in a vinyl pool.

 

[Guest]

Ok, I will toss in my 2 cents on the pH and CH issues.

pH: I think the wider range of 7.2-7.8 is more practical for the average user, as long as that does not cause any damage. The benefits of a tighter range can be discussed elsewhere. I am pretty sure I have suggested 7.2-7.6 in the past. And now that i think about it, are most scales not in increments of 0.2 ppm? So to ask for 7.5 would just be a guess anyway.
Not for someone using either the TF100 or Ben's PS234. It has a color chip at 7.5! This is why I said 7.5 instead of 7.6. Keeping the pH at the higher end of the scale will lead to less acid demand. Most beginners make the mistake of dropping the ph to the low end thinking that it will give them more time before they need to add acid again.
We know that isn't true! (At least those of us who have ever lowered TA know that )
AND, don't we always say a lower pH allows the chlorine to be more effective? I think of 'low' as 7.2-7.4.....
Not true once CYA is in the picture, only really true in an unstabilized pool!
Hey, the smilies are back!

CH: I was not aware that there was an actual minimum for vinyl (and I just barely remember it for FG now that you mention it.) Just not to let it get TOO high because of scaling issues. (I believe on PF it was stated not to worry unless it got over 400 or maybe even 500?) Now, there may have been other discussions that I just did not follow on the merits of SOME CH in a vinyl pool.

High calcium is almost a non issue IF the pH is kept under control, once again reason for the smaller pH range I suggested. It makes high calcium much less of an issue. pH is the MAIN factor that will predict scaling. At high ph scaling can occur with 'normal' calcium levels! pH control is really the key. Teach people right from the beginning how to control and maintain pH and you eliminate a lot of other problems associated with water balance and make pool maintenance much easier!
The reason for a minimum recommendation of Ch for vinyl pools is twofold:
First, many people are under the mistaken assumption that just because vinyl pools do not need calcium to protect the finish (which both plaster and fiberglass do) that it is not important to test and know their calcium levels. We know that is not true. For example, if they have high calcium and they add baking soda they can end up with cloudy water and not know why! Just because they don't NEED the calcium doesn't mean they don't need to KNOW where their calcium is.
Second, if they are filling with soft water their pools might have more of a tendency to foam. Soft water foams easier than hard water (Isn't that the reason we install water softeners, to make our water lather faster when we add a surfactant?) The organics that enter our water are surfactants (soaplike). If we have SOME hardness to the water the water is less likely to foam. One person at PF has said that chlorine alone will take care of this because it works in his pool (but he is meticulous about maintaining his pool daily and we KNOW that not all people are!) but I have a lot of customers with vinyl pools and those with soft water did have foaming problems until we raised their calcium hardness above 100. I chose 120 ppm just to give a 'safety margin'. It's an easy fix to prevent a common problem, expecially when someone is still learning to maintain their FC levels. This also applies to stand alone acrylic hot tubs, which don't need calcium either BUT if they have a hardness less than about 150 ppm you will definitely see a lot of foaming!

 

[SeanB]

I like the last chart above, minus the trichlor, discussed as a footnote.

On levels, unless harm is going to be done, I'm in favor of broader ranges - easier to reach and easier to maintain.

 

[JasonLion]

SeanB - Do you mean that you like the most recent iteration of the nine table chart at the top of page 2 of this thread, except with the trichlor column removed, so really a six table chart?

On PH

The TF-100 and many of the cheap kits have PH color standards for 7.2, 7.5, and 7.8. The Taylor K-2006 has color standards for 7.2, 7.4, 7.6, and 7.8. (There are also other color standards outside that range, but they are not relevant to this discussion.)

When PH drift is caused by high TA and aeration, the rate of drift is much faster at lower PH. Lowering PH to 7.2 instead of 7.5 does get you just a tiny bit more time, but nothing like twice as long. By lowering PH to 7.2 you also lower the TA by more then you would with the smaller PH change. That also adds just a little more time till PH is high again and more significantly reduces the amount of time and number of cycles till TA levels are more reasonable.

When PH drift is caused by plaster curing you do get noticeably more time by lowering the PH further. Likewise when PH drift is caused by trichlor, waiting to raise PH until the PH is down closer to 7.2 gives you noticeably more time till the next time you need to raise PH.

Lower PH levels when shocking are not that important for killing algae when there is CYA in the water. However, if PH starts around 7.8, and you then add 15 ppm of FC using bleach, the PH will shoot up rather dramatically, up towards 8.6 assuming TA around 100, for a short while before the FC gets consumed. In some situations that can trigger metal stains and other problems. The periods of high PH are usually short, so normally nothing happens, but sometimes the effects are significant.

One final advantage of recommending a default range that goes down to 7.2 is that you don't create an an appearance of a contradiction between the recommendation and the various situations when PH should be lower, such as an ascorbic acid treatment, baquacil conversion, etc. People do weird and unpredictable things when you tell them to go outside published ranges, assuming they put any faith in the published range. You are asking them to ignore one set of instructions in favor of another, and they don't always ignore the one they should be ignoring.

On CH

Reports of CH levels around zero are very rare. However reports of CH levels in the 50 to 100 range are more common, for example here, here, and here. None of those people are reporting foaming. Foaming isn't exactly a common issue, despite years of PF recommending low CH with vinyl, nearly all of the existing foaming reports are for a spa or after adding the wrong kind of algaecide.

Ben has always been adamant that CH is not required for vinyl pools. It seems very reasonable to assume that he had experience with CH levels below 100 since he normally based his recommendations on his personal experience.

I agree that people neglecting to test for CH at all are way too common. Between that, the lack of experience with CH below 50, and chem geeks fears about corrosion, I have no problem putting the lower bound at 50.

 

[Guest]

Ben has always been adamant that CH is not required for vinyl pools. It seems very reasonable to assume that he had experience with CH levels below 100 since he normally based his recommendations on his personal experience.

He also stated that this applied to fiberglass pools because he assumed that the only fact was protecting the calcium in plaster pools and I have researched this matter which is why I raised the level in my own pool and recommend that fiblerglass be run at higher CH to help prevent cobalt spotting and staining.

 

[SeanB]

SeanB - Do you mean that you like the most recent iteration of the nine table chart at the top of page 2 of this thread, except with the trichlor column removed, so really a six table chart?

Yes.

 

[Guest]

FYI, post58137.html#p58137
THIS is why I suggest a more narrow pH range. Once people learn how to do it it's easy. just ask any of my customers.

 

[JasonLion]

Reducing everything to a single range requires combining a number of different ideas. Examining PH:

* Eye irritation and calcium scaling risk issues suggest a range of 7.2 to 7.8.
* When PH does not drift significantly, the ideal range is traditionally though of as 7.4 to 7.6.
* When PH drifts due to high TA and aeration, PH is most stable around 7.6 to 7.8.
* When PH drifts due to plaster curing or trichlor, 7.2 to 7.8 is much simpler to manage. In extreme cases of rapid plaster curing in the first three week, allowing a range of 7.0 to 8.0 is sometimes required as a practical matter.
* PH of 7.2 to 7.4 is preferred when metal staining is a significant problem and is often critical with copper ionizers.

Should a recommended range cover all (or most) of these cases? Or should it provide more specific guidance for the most common of these situations? A narrow default range can lead to confusion for people with one of the situations that it does not cover. On the other hand, a wide default range can cause confusion for people with the most common situation(s) requiring a narrower range (who now need to look in two places).

This also interacts with the number of tables used in the presentation. In the 9 (or 6) table version it is plausible to expect SWG users to have high TA/aeration issues and so list the narrower range for that situation in the SWG tables. But in the one and three table versions the conflicts are more apparent, since none of the issues affecting the ideal range are broken out.

 

[Guest]

Reducing everything to a single range requires combining a number of different ideas. Examining PH:

* Eye irritation and calcium scaling risk issues suggest a range of 7.2 to 7.8.
Actualy, higher levels of pH up to about 8.0 are the most 'eye comfortable' (http://www.poolsolutions.com/tips/tip72.html Read the last line on that page.)(
* When PH does not drift significantly, the ideal range is traditionally though of as 7.4 to 7.6.
* When PH drifts due to high TA and aeration, PH is most stable around 7.6 to 7.8.
Most people using bleach or other unstabilized chlorine sources will ususally see a bit of pH rise, not all but the majority, so the second one becomes more inclusive.
* When PH drifts due to plaster curing or trichlor, 7.2 to 7.8 is much simpler to manage. In extreme cases of rapid plaster curing in the first three week, allowing a range of 7.0 to 8.0 is sometimes required as a practical matter.
Curing new plaster is NOT normal pool maintenance, it's new pool startup and it's a different animal in several respects!
* PH of 7.2 to 7.4 is preferred when metal staining is a significant problem and is often critical with copper ionizers.
Metal staining usually is not a problem with pH below 7.8 ,but even if the pH needs to be dropped we are dealing with a special case and NOT normal pool maintenance! As far as ionizers go we are dealing with chlorine sanitized pools here, not pools with ionizers. They are definitely a special case!
Should a recommended range cover all (or most) of these cases? Or should it provide more specific guidance for the most common of these situations? A narrow default range can lead to confusion for people with one of the situations that it does not cover. On the other hand, a wide default range can cause confusion for people with the most common situation(s) requiring a narrower range (who now need to look in two places).
My feeling is that recommended ranges should cover what is considered to be normal pool maintenance. This will exclude new plaster startup, metal staining, ionizers, etc.

This also interacts with the number of tables used in the presentation. In the 9 (or 6) table version it is plausible to expect SWG users to have high TA/aeration issues and so list the narrower range for that situation in the SWG tables. But in the one and three table versions the conflicts are more apparent, since none of the issues affecting the ideal range are broken out.

I don't seem to follow that last paragraph you wrote :?: Could you explain what you mean? I don't see any conflicts in the ranges for a three table version (assuming one is for vinyl, one for fibeglass, and one for plaster).

 

[JasonLion]

I don't seem to follow that last paragraph you wrote :?: Could you explain what you mean? I don't see any conflicts in the ranges for a three table version (assuming one is for vinyl, one for fibeglass, and one for plaster).

I was saying that the situation of "high TA/aeration" is so common with a SWG that it makes a great deal of sense to use the 7.5 to 7.8 range for PH in the SWG column of the 9 (or 6) table version, even if I disagree with using that range with bleach and trichlor. With the one or three table (vinyl/fiberglass/paster) versions, the 7.5 to 7.8 range seems to me to apply to less than half of all pools. In my mind that makes it a special case to be put in a footnote.

The common case where PH between 7.5 and 7.8 makes the least sense to me is using bleach without any source of aeration, ie no SWG, waterfall, spa, or fountain. This is probably somewhere around 40% of all pools at TFP. While there is often some PH drift in these pools, it is normally slow enough to be unimportant and it isn't clear that it comes from TA/aeration.

In these pools, using a wider range is simpler and requires less frequent chemical additions. Also, the plaster pools in this group benefit from the wider range by gaining some additional margin (on average) before scaling becomes an issue. Plaster less than one year old also adds to the value of the wider range for a fair portion of these people. Trichlor users are probably another 5+%.

I worry about telling people to lower their PH below 7.5, which comes up fairly frequently, when there is an obvious recommended level chart showing 7.5 to 7.8 as the recommended range. It makes much more sense to me to tell people to use a narrower range because they have aeration, even if the fraction of people in this situation approaches 50%.

 

[chem geek]

I think both general situations can be covered by having a "Trouble Free" set of recommendations that are simple and will work in most cases, so would be the 7.5 to 7.8 pH range and a low TA (80-100) using mostly hypochlorite chlorine sources and CYA at 30-50 for non-SWG and 60-80 for SWG. Then one can have an "Advanced" set of ranges with more explanations and caveats, special situations, etc.

Richard

 

[Guest]

I think both general situations can be covered by having a "Trouble Free" set of recommendations that are simple and will work in most cases, so would be the 7.5 to 7.8 pH range and a low TA (80-100) using mostly hypochlorite chlorine sources and CYA at 30-50 for non-SWG and 60-80 for SWG. Then one can have an "Advanced" set of ranges with more explanations and caveats, special situations, etc.

Richard

Thank you Richard, that's what I've been saying!

 

[SeanB]

I'm for whatever set of numbers you all can agree upon that will be the easiest to follow and cover the greatest number of people without having to list exceptions.

I think the table looks nice as a reference but am having a hard time seeing people posting that within their threads. I think the main point is to pick a range for each parameter that is going to cover the greatest number of people, without doing harm to any particular group, and use those as a baseline for advice so that we have a commong starting point.

Let's try this - with no other explaination or debate, whomever would like to contribute - list the parameter and the recommended range. We'll see what we have in common and go with that.

 

[JasonLion]

Alright, PH from 7.5 to 7.8.

(EDIT)Sorry SeanB, I think the great majority of the ranges are well agreed upon. There are some minor quibbles unresolved, but really they are minor and we are very close. Everything can be put into one table with a two part answer for CH if that is simpler to quote, though that doesn't seem like the best choice for the recommended levels Pool School article.(/EDIT)

Trying to bring the discussion together into one place, allowing that I might have missed some comments or have a typo, here are the two leading layouts and my sense of the consensus level proposals. Having six tables allows us to fine tune the SWG case a little more, at the expense of an increase in complexity.

[tr:37oa1egz][td:37oa1egz] Vinyl [/td:37oa1egz][td:37oa1egz] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 50-300
  CYA 30-50

[/td:37oa1egz][td:37oa1egz] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 50-300
  CYA 70-80

[/td:37oa1egz][/tr:37oa1egz][tr:37oa1egz][td:37oa1egz] Plaster [/td:37oa1egz][td:37oa1egz] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 250-350
  CYA 30-50

[/td:37oa1egz][td:37oa1egz] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 250-350
  CYA 70-80

[/td:37oa1egz][/tr:37oa1egz][tr:37oa1egz][td:37oa1egz] Fiberglass [/td:37oa1egz][td:37oa1egz] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 220-320
  CYA 30-50

[/td:37oa1egz][td:37oa1egz] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 220-320
  CYA 70-80

[/td:37oa1egz][/tr:37oa1egz][/table:37oa1egz]

and

Vinyl and paint

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 50-300
  CYA 30-50 (70-80 for SWG)

Plaster, pebble, quartz, gunite

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 250-350
  CYA 30-50 (70-80 for SWG)

Fiberglass

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 220-320
  CYA 30-50 (70-80 for SWG)

Rough draft of footnotes:

These levels will work for most pools most of the time, but are not ideal in all situations. For recommendations on what would be ideal for your pool please ask for advice on the forum.

If you are using trichlor tablets for chlorine, follow the bleach recommendations but raise TA to 100-120 and be sure it doesn't fall below 100. [[No mention of bleach in the three table version.]]

If you have high levels of CH in your fill water, it is possible to manage CH levels up to about 1,200 to reduce the frequency of replacing water. High CH levels require careful control over PH and TA level at all times. See [[article not yet written]] for more information.

For pools that get direct sunlight the entire day, is is sometimes best to raise CYA to the 70-80 range, even if you don't have a SWG, to reduce the amount of chlorine lost to sunlight.

Pools with a large amount of aeration, common with a negative edge, large waterfalls, and/or several fountains, can help control constant PH increases by lowering TA to around 60 and adding borates.

Plaster, pebble, quartz, and gunite pools that are less than one year old should expect to see constant PH increases and slower increases of TA and CH. This process is very rapid for the first three or four weeks and then continues more slowly for up to a year.

 

[chem geek]

[tr:3hh14rkg][td:3hh14rkg] Vinyl [/td:3hh14rkg][td:3hh14rkg] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 50-300
  CYA 30-50
  SI -0.90 to +0.31 (mid-point -0.13)

[/td:3hh14rkg][td:3hh14rkg] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 50-300
  CYA 70-80
  SI -1.33 to -0.06 (mid-point -0.53)

[/td:3hh14rkg][/tr:3hh14rkg][tr:3hh14rkg][td:3hh14rkg] Plaster [/td:3hh14rkg][td:3hh14rkg] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 250-350
  CYA 30-50
  SI -0.23 to +0.36 (mid-point +0.08)

[/td:3hh14rkg][td:3hh14rkg] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 250-350
  CYA 70-80
  SI -0.65 to +0.00 (mid-point -0.31)

[/td:3hh14rkg][/tr:3hh14rkg][tr:3hh14rkg][td:3hh14rkg] Fiberglass [/td:3hh14rkg][td:3hh14rkg] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 220-320
  CYA 30-50
  SI -0.28 to +0.33 (mid-point +0.04)

[/td:3hh14rkg][td:3hh14rkg] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 220-320
  CYA 70-80
  SI -0.70 to -0.04 (mid-point -0.35)

[/td:3hh14rkg][/tr:3hh14rkg][/table:3hh14rkg]

and

Vinyl and paint

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 50-300
  CYA 30-50 (70-80 for SWG)
  SI -0.90 to +0.31 (-1.22 to +0.01 for SWG)

Plaster, pebble, quartz, gunite

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 250-350
  CYA 30-50 (70-80 for SWG)
  SI -0.23 to +0.36 (-0.53 to +0.07 for SWG)

Fiberglass

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 220-320
  CYA 30-50 (70-80 for SWG)
  SI -0.28 to +0.33 (-0.59 to +0.03 for SWG)

I know that the saturation index is not that picky, but some of the ranges we've got aren't appropriate. I list the saturation index for the above using the extremes for each parameter and for the main table the mid-points. The index is most important for plaster pools, less important for fiberglass, and not important for vinyl. I assumed 525 ppm TDS for bleach and 3200 ppm TDS (3000 ppm salt) for SWG and I used 85F for temperature.

Basically, the ranges and mid-points for bleach are OK, but for SWG they are too low, especially for plaster and fiberglass where it makes a difference. The SWG pool's higher salt level as well as the higher CYA level (at the same TA level) makes it more likely to pit plaster so the pH, TA or CH factors must be higher to compensate. You actually have the TA range lower than with bleach, mostly to reduce the effects of outgassing, but I've never recommended going down to 60 ppm unless other parameters are higher such as CH. I would make two changes for SWG pools. First is to have the TA range be 70-80 ppm instead of going down to 60 ppm. Second, is to have the CH range be 350-450 ppm. These two changes would make the SI range for plaster pools go from -0.39 to +0.10 with a mid-point of -0.14 which seems more reasonable to still avoid scaling in the SWG. What do y'all think?

Richard

 

[JasonLion]

Indeed. Good catch Richard!

In case anyone is confused, Richard is not suggesting adding saturation index to the tables. He listed them so we could see if any of the other numbers should be changed.

These observations support the six table layout, since it is mostly the SWG numbers that need work and having the separate SWG tables makes for a much simpler fix.

I have been working with a number of people to lower TA further and further to reduce PH drift in high aeration situations. I normally recommend raising CH levels when this is done, but failed to factor that into this discussion.

For plaster/SWG, making the CSI adjustment to take it all the way to balanced around zero entirely with calcium requires the rather dramatic CH range of 500-600. CH from 400-500 is probably plenty in practice, but even that gives one pause.

One thing to keep in mind is that the "traditional" chemical level recommendations have significantly wider CSI ranges, because they have wider ranges for nearly every individual level.

 

[Guest]

[tr:2vust3t7][td:2vust3t7] Vinyl [/td:2vust3t7][td:2vust3t7] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 50-300
  CYA 30-50
  SI -0.90 to +0.31 (mid-point -0.13)

[/td:2vust3t7][td:2vust3t7] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 50-300
  CYA 70-80
  SI -1.33 to -0.06 (mid-point -0.53)

[/td:2vust3t7][/tr:2vust3t7][tr:2vust3t7][td:2vust3t7] Plaster [/td:2vust3t7][td:2vust3t7] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 250-350
  CYA 30-50
  SI -0.23 to +0.36 (mid-point +0.08)

[/td:2vust3t7][td:2vust3t7] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 250-350
  CYA 70-80
  SI -0.65 to +0.00 (mid-point -0.31)

[/td:2vust3t7][/tr:2vust3t7][tr:2vust3t7][td:2vust3t7] Fiberglass [/td:2vust3t7][td:2vust3t7] with Bleach

• 
  FC 3-7
  pH 7.5-7.8
  TA 70-90
  CH 220-320
  CYA 30-50
  SI -0.28 to +0.33 (mid-point +0.04)

[/td:2vust3t7][td:2vust3t7] with SWG

• 
  FC 3-5
  pH 7.5-7.8
  TA 60-80
  CH 220-320
  CYA 70-80
  SI -0.70 to -0.04 (mid-point -0.35)

[/td:2vust3t7][/tr:2vust3t7][/table:2vust3t7]

and

Vinyl and paint

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 50-300
  CYA 30-50 (70-80 for SWG)
  SI -0.90 to +0.31 (-1.22 to +0.01 for SWG)

The SI is fine for a vinyl pool. Most vinyl pools that are being run with very low TA have 'corrosive' SI when you calculate it but it seems to have no adverse effects and with a SWG it wil lhelp prevent calcium scaling! Plaster, pebble, quartz, gunite

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 250-350
  CYA 30-50 (70-80 for SWG)
  SI -0.23 to +0.36 (-0.53 to +0.07 for SWG)

These SI numbers are fine. You usually want a salt pool to be slightly corrosive to help prevent scale formation. These numbers are certainly in line! Fiberglass

• 
  FC 3-6
  pH 7.5-7.8
  TA 70-90
  CH 220-320
  CYA 30-50 (70-80 for SWG)
  SI -0.28 to +0.33 (-0.59 to +0.03 for SWG)

See what I said about vinyl pools above!
I know that the saturation index is not that picky, but some of the ranges we've got aren't appropriate. I list the saturation index for the above using the extremes for each parameter and for the main table the mid-points. The index is most important for plaster pools, less important for fiberglass, and not important for vinyl. I assumed 525 ppm TDS for bleach and 3200 ppm TDS (3000 ppm salt) for SWG and I used 85F for temperature.
Most salt pools will have a higher TDS than this. Figure on a 'normal TDS of around 600 ppm plus a salt level of anywhere from 3000-4000 ppm (depending on SWG brand).
Basically, the ranges and mid-points for bleach are OK, but for SWG they are too low, especially for plaster and fiberglass where it makes a difference.
How does it make a difference for fiberglass? It has a non reactive surface.
The SWG pool's higher salt level as well as the higher CYA level (at the same TA level) makes it more likely to pit plaster so the pH, TA or CH factors must be higher to compensate. You actually have the TA range lower than with bleach, mostly to reduce the effects of outgassing, but I've never recommended going down to 60 ppm unless other parameters are higher such as CH. I would make two changes for SWG pools. First is to have the TA range be 70-80 ppm instead of going down to 60 ppm.
I originally said 70-90!
Second, is to have the CH range be 350-450 ppm. These two changes would make the SI range for plaster pools go from -0.39 to +0.10 with a mid-point of -0.14 which seems more reasonable to still avoid scaling in the SWG. What do y'all think?
From practical experience I can tell you that having calcium in this higher range WILL lead to scaling because most SWG owners do let their pH spike above 8.0...I see it all the time.

review my orginal post on this subject:

How about this:
Plaster pool
FC 3-5
pH 7.5-7.8
TA 70-90 unstabilized CL and SWG
100-120 stabilized CL
CH 250-350 (I give a smaller range because the ends of the range 200-400 can quickly become special cases, particularly if there is a testing error, which is common with newbies.)
CYA 30-50 (70-80 for SWG)

Fiberglass
FC 3-5
pH 7.5-7.8
TA 70-90 unstabilized CL and SWG
100-120 stabilized CL
CH 220-320 (This is actually in line with most of the major fiberglass manufacturers who recommend ranges from 175-225 to the standard 200-400)
CYA 30-50 (70-80 for SWG)

Vinyl
FC 3-5
pH 7.5-7.8
TA 70-90 unstabilized CL and SWG
100-120 stabilized CL
CH 120-350
CYA 30-50 (70-80 for SWG)

IMHO, you are all overthinking this!!

 

[JasonLion]

From practical experience I can tell you that having calcium in this higher range WILL lead to scaling because most SWG owners do let their pH spike above 8.0...I see it all the time.

An excellent point! Many people with any aeration will allow their PH to go up to 8.4 at some point. Unless they are using trichlor it is remarkably unlikely that they will have their PH go down dramatically. Except for trichlor users, it makes a great deal of sense to bias things so that a PH of 8.4 is not a serious problem.

Trichlor users have almost the exactly opposite effect, low PH is likely and high PH is unlikely. Perhaps all we need is an additional note in the trichlor footnote to do something that raises SI when using trichlor.

 

[chem geek]

I thought that fiberglass needed some degree of saturation of calcium carbonate to protect the gelcoat. If that's not true, then it's more like vinyl where the low SI doesn't matter. I only put the low numbers in red to make them obvious, not to say they were a problem in all situations. I wrote that it wasn't a problem for vinyl.

So the question is whether -0.65 is too low for a plaster pool. I agree that you want somewhat corrosive water for the SWG to prevent scaling. If the pH really does get to 8.0 or higher with an SWG, then maybe instead of a higher CH the solution is to recommend a higher pH range that is easier to manage and where pools will end up anyway. So instead of 7.5 to 7.8, for an SWG it would be 7.7 to 8.0. That would have the SI be -0.47 at the low end to +0.19 at the high end if the low TA recommendation were 60, but if it were 70 then the low would be -0.35 at 3000 ppm salt and -0.40 at 4000 ppm salt.

If we don't change the pH recommendation but do change just the low TA to 70, then that's an SI of -0.53 for 3000 ppm salt and -0.58 for 4000 ppm salt.

Since there are measurement errors and even the SI calculations aren't consistent (the one I use that matches the Taylor watergram is lower by about 0.10 then the one based on info quoted by Wojtowicz I recently received) I just wanted to be a little on the safer side closer to the middle, but I agree that for SWG pools we want the ranges to be in the negative SI area regardless of how we accomplish that.

Richard

 

[Guest]

I thought that fiberglass needed some degree of saturation of calcium carbonate to protect the gelcoat. If that's not true, then it's more like vinyl where the low SI doesn't matter. I only put the low numbers in red to make them obvious, not to say they were a problem in all situations. I wrote that it wasn't a problem for vinyl.
There seems to be some evidence that higher calcium levels prevent cobalt spotting (black pinpoints that grow almost like a crystal into a small nodule--only happens in fiberglass pools and the newer gelcoats do seem to have minimizes this to an extent) and do help prevent staining (both Mbar and myself have seen this in our own fiberglass pools) and most fiberglass manufacuters do recommend a slighly lower CH range than is commonly given for plaster but I have not been able to come up with anything definitive even though I have been researching this for about 3 years now.

So the question is whether -0.65 is too low for a plaster pool. I agree that you want somewhat corrosive water for the SWG to prevent scaling. If the pH really does get to 8.0 or higher with an SWG, then maybe instead of a higher CH the solution is to recommend a higher pH range that is easier to manage and where pools will end up anyway. So instead of 7.5 to 7.8, for an SWG it would be 7.7 to 8.0. That would have the SI be -0.47 at the low end to +0.19 at the high end if the low TA recommendation were 60, but if it were 70 then the low would be -0.35 at 3000 ppm salt and -0.40 at 4000 ppm salt.
The only reason I picked 7.5 is because that is a color chip on the TF100 test block. I actually prefer 7.6 to 7.8 for the range. This gives some breathing room because many people won't catch the pH until it hits 8.0 so this gives a safely margin. I don't really like an SI more corrosive than -.5 but many published tables for SI in the industry say that -.7 to .7 is ok. It depends on who you talk to. I still feel that SI is a good predictor of scaling but not as good at predicting plaster damage and that low pH is going to be more likely to cause etching than having a SI that is on the 'corrosive' side. If you remember, Ben Powell did not put much stock into the SI either and he had a lot of experience with pools.

If we don't change the pH recommendation but do change just the low TA to 70, then that's an SI of -0.53 for 3000 ppm salt and -0.58 for 4000 ppm salt.
Which is what I originally said!

Since there are measurement errors and even the SI calculations aren't consistent (the one I use that matches the Taylor watergram is lower by about 0.10 then the one based on info quoted by Wojtowicz I recently received) I just wanted to be a little on the safer side closer to the middle, but I agree that for SWG pools we want the ranges to be in the negative SI area regardless of how we accomplish that.

Richard

Once again, there seems to be a lot of empirical evidence that low pH is more likely to cause etching than a slighly low SI.