Turning the SWG off during SLAM

AUSpool

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Sep 23, 2015
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I personally think that the initial pH-rise when getting to SLAM levels, can be quite tricky. As an example, take a 50000l salt water pool at CYA=80, TA=70, CH=450, salt=4000, FC=6. Nicely balanced water at pH=7.7 and 77°F. Now, you first get pH down to 7.2, which gets your CSI briefly down to -0.66 (I am using the Poolequations.xls here, PoolMath is slightly higher). Now you add 10l of 12.5% strength bleach to get to the SLAM level of FC=31 for that CYA. This will boost your pH up to 8.54 (and you will stay there while adding more chlorine to maintain shock level), resulting in a CSI of +0.69 (again, a bit higher with PoolMath). If you have your SWG running as well, the pH will be even higher within the cell (the temperature will probably also be slightly higher there), and the increased out-gassing due to running the SWG will increase the pH even further (probably not hugely, as out-gassing should slow down at high pH). Sounds like a recipe to create calcium scaling in the cell.
Where did you get a pH of 8.54 from? I cant see you getting up to a pH of 8.54 and staying there, 10L of 12.5% hydroxide will get you to 9. Variation in temps and pH within the cell are a bit theoretical, in reality you’ll find the pH and temp within the cell is the same as the pool water. The new Insnrg chlorinators have their pH probe ports in the cell and found during product testing that there was no variation between the cell and pool water.


How do you know remotely that the cell is actually producing what it's supposed to according to the data sheet? How worn out are the electrodes, how much scaling?
What do you mean by remotely? I think your over thinking it. You know the SWG is producing FC because of your constant FC test results. If I’m running high I turn my SWG down a bit, if I’m low I turn it up a bit. Actually if I low bring my FC up to my target with bleach and turn my SWG up a little.

One of TFP’s SLAM prerequisites is that the pump is run 24/7 and it’s very hard for the average user to manage FC with a SWG when the pump is running 24/7. Whilst I may choose to alter the SLAM process for my own use the best advise is to recommend to turn the SWG off as per the SLAM article.
 

mgtfp

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Mar 5, 2020
288
Melbourne, Australia
Where did you get a pH of 8.54 from?
That was calculated with ChemGeek's PoolEquations for the example in my earlier post, assuming that pH is 7.2 before adding bleach:

PoolEquations.png

If I assumed that the pH started at 7.7, then I actually needed to add first enough muriatic acid to bring the pH down to 7.2, which would also bring TA down to about 62, resulting in a larger pH rise to 8.64 after adding 10l of 12.5% bleach. PoolMath might give different results, but I believe that PoolEquations will be more accurate than PoolMath.

What do you mean by remotely?
That was speaking from the perspective of a TFP-Guide who is remotely assisting a new TFP-member during a slam, trying to assess the chlorine loss and recommend what to do based on the information given via the forum.

Whilst I may choose to alter the SLAM process for my own use the best advise is to recommend to turn the SWG off as per the SLAM article.
That was also my conclusion. If you know what you are doing you may chose to alter the slam guidelines to suit your needs. But the general guideline of turning off the SWG during the slam creates normalized conditions, that enable new members without prior TFP experience to successfully slam their pool with the assistance of a TFP-guide.
 

calinb

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Jul 18, 2018
116
N. Central, ID
One of TFP’s SLAM prerequisites is that the pump is run 24/7 and it’s very hard for the average user to manage FC with a SWG when the pump is running 24/7.
My Core35 SWG simply plugs into a 110 VAC GFCI outlet so I put a wall timer in the outlet to insure it only comes on when the pump timer is set to run the pump (a safety precaution in case the Core35 water flow switch fails). So it's really easy for me to manage the SWG, with or without the pump running 24/7. Hard wired SWGs might be slightly more difficult to control, which is another reason that I like my Circupool Core 35 over more complex or highly system-integrated SWGs, but turning an SWG on and off seems to me to be as just easy as adding jugs of LC, and another source of Cl will almost certainly still be necessary in the early hours (days?) of a SLAM while the SWG runs 100%/24 hours. The SWG just creates a negative offset in the SLAM chlorine demand that must be met with supplementation (sort of like having a less swampy swamp to clear).

It only took me one night of 100% SWG production to learn that my SWG was putting out the quantity of Cl the manufacturer claimed in its specs ($7.58 worth of Wally World LC per day). I can also get an indirect idea of how much Cl it's producing by looking at the flow of tiny bubbles from the returns, which vary with the output setting on the SWG panel. A laser pointer shone through the clear cell housing also provides an indirect and somewhat subjective measurement.

I've cleared a green pool three times with SLAM now. Once when I bought the pool, once during an early opening this year, and once out of the blue (green?) after opening after the pool had remained covered during a bad turn in the weather. I believe the last two problems were the direct result of the combined chlorine effects and post-treatment challenges imposed by Jack's #2 (sulfamic acid) stain treatment. For the last SLAM I used my SWG as much as possible. It was the easiest SLAM of them all, requiring the lowest level of participation and active management. Supposedly SWGs "supercharge" the disinfectant power of chlorine as water passes by the cells. Perhaps this kills algae spores better too. I'm just speculating and I have no empirical evidence that it does so but it's something to consider.
 

Newdude

Well-known member
Jun 16, 2019
3,756
NY
Supposedly SWGs "supercharge" the disinfectant power of chlorine as water passes by the cells. Perhaps this kills algae spores better too. I'm just speculating and I have no empirical evidence that it does so but it's something to consider
It’s the constant production. If it’s properly oversized it will just fight the battle for you. There won’t be lags or overnight drops because you didn’t wake up 3 times to dose or were busy at work during the day. The first day or two you may need to help it when the algae is at its strongest but after that it just chugs along on it’s own.

But if you don’t teach a newb what they need to be doing, They will be back in 3 weeks. And 3 weeks after that.
 
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AUSpool

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That was calculated with ChemGeek's PoolEquations for the example in my earlier post, assuming that pH is 7.2 before adding bleach.

...

If I assumed that the pH started at 7.7, then I actually needed to add first enough muriatic acid to bring the pH down to 7.2, which would also bring TA down to about 62, resulting in a larger pH rise to 8.64 after adding 10l of 12.5% bleach. PoolMath might give different results, but I believe that PoolEquations will be more accurate than PoolMath.
The theoretical change to pH is only accurate at 7.2 - 7.8 with a TA between 80 - 120ppm and no borates. Beyond that the calculations become unreliable. I believe it was ChemGeek that didn’t transfer the pH affect from PoolEquations to PoolMath due to the unreliable nature of the calculations.

I’m not sure you can remotely manage someone’s SWG. The best you can do is offer the best advise based on the given information which is why we ask for test results from one of the recommended kits.
 

mgtfp

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Mar 5, 2020
288
Melbourne, Australia
The theoretical change to pH is only accurate at 7.2 - 7.8 with a TA between 80 - 120ppm and no borates. Beyond that the calculations become unreliable. I believe it was ChemGeek that didn’t transfer the pH affect from PoolEquations to PoolMath due to the unreliable nature of the calculations.

I’m not sure you can remotely manage someone’s SWG. The best you can do is offer the best advise based on the given information which is why we ask for test results from one of the recommended kits.
Didn't know that. The point I wanted to make in that post was that pH will be quite high after adding 25ppm worth of bleach until those 25ppm will be used up. It will be somewhere between 8 and 9, I guess. The exact value doesn't really matter, apart from being quite high. My understanding is that it will stay there while you keep adding bleach to keep FC at this level. Once FC goes back to normal, pH will be back to it's pre-slam value (plus aeration drift that happened in the meantime).

I wasn't talking about remotely managing someone else's SWG. I was talking about a TFP guide helping a new TFP member with a slam. I just called that "remote" because the guide will be at a different location. This guide will want to estimate chlorine losses based on FC-testing and how much chlorine was added in a certain period of time. This will be easier when the chlorine comes only from one source, with the SWG being turned off.
 

duraleigh

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Background is the question if the SWG should be turned off during a SLAM or not.
Turn the SWG off.......period.

1. The acronym SLAM was chosen to imply a sudden large dose of chlorine to get the process started and the SWG can not do that.

2. Probably half the newbies who start a SLAM don't do it correctly because they misunderstand the need to keep FC at SLAM value.

3. The SWG only aggravates that situation by giving them a false sense of, "well, the SWG is on so that should take care of it" We've seen that hundreds and hundreds of times

4. SWG on "masks" the chlorine loss to the newbie and gives him a sense he is keeping up when he is not. Real chlorine loss becomes confusing to the newbie.

5. It's easy after you "get it" on TFP to implore others to "get it", also. YOu slip into abbreviations the newbie doesn't understand. You assume the newbie knows things that you have known for a couple of years.......he doesn't he hasn't been here a couple of years and the concepts (like combining LQ and SWG production during a SLAM are foreign to him.

6. Everything on this forum should be taught in the simplest of terms. (Each time I post that, I get back, " Oh, I don't think this is complicated at all!" That's smug and annoying and incorrect. A brain surgeon probably doesn't think brain surgery is all that complicated, either.)

Throughout the forum, we see things like mistakenly adding dichlor not understanding the CYA price that is paid. Adjusting multiple parameters with one dose is easy-peasy when you have been on here a while.......troublesome for the newbie. Leaving the SWG on during a SLAM falls in that category. Teach the SLAM on the level of the student......not on the level of the teacher.
 

AUSpool

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Edit: Thanks Dave, Good points.

Back to @mgtfp’s last post

Thats why I raised it because I don’t think your pH will go that high. I doubt it would get as high as 8 and stay there for the duration of the slam. But I’m no expert, for that I would have to ask @JoyfulNoise for his thoughts.
 
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mgtfp

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Mar 5, 2020
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Melbourne, Australia
Thanks @AUSpool for passing that on, let's see if Matt can shed some light on that. I always thought that ChemGeek's sheet would be accurate enough to at least trust the pH calculation that far that the pH rise would be quite significant for a 25ppm worth bleach dump, which is part of the reason why it's so important to lower pH to 7.2 before going up to slam level. pH goes down once algae and UV reduce FC, but rises again when adding more bleach to get back to slam-level.

To Dave's summary regarding the SWG question is nothing to add, very good conclusion. And that was more or less what @Newdude , @mguzzy and I also concluded in our discussion, maybe it didn't get clear enough in my lengthy post. Thanks @duraleigh for clarifying that,
 

Newdude

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Jun 16, 2019
3,756
NY
And that was more or less what @Newdude , @mguzzy and I also concluded in our discussion, maybe it didn't get clear enough in my lengthy post. Thanks @duraleigh for clarifying that,
Dave aptly put the exclamation point on our discussion. Well done as always sir !!
 

mgtfp

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Mar 5, 2020
288
Melbourne, Australia
Hey @AUSpool ,

I think the SWG discussion has been closed thanks to Dave, there is nothing to be added.

I just wanted to quickly get back to the topic of the pH-rise. There are a number posts from chem geek where he calculated a pH-rise to above 8 after adding bleach (or cal-hypo). He usually pointed out in his posts that pH gets back down to the previous level once the added chlorine gets used (neglecting other effects on pH). But in one post that I found he also highlighted that pH would remain high if the higher FC level was being maintained (in this case, FC was increased because the TFP member had learnt about the CYA/FC table and adjusted FC to his 90+ CYA):

Adding chlorine DOES raise the pH, but when the chlorine gets used/consumed the pH drops back down. Specifically, starting with your numbers I calculate that the pH would have risen from 7.6 to 8.2. Also, if you read the pH test fairly quickly, then 13.6 ppm FC isn't going to give you a false reading. Your pH is very likely to be at 8.2 if your initial reading was correct (not sure why you think it's 7.8).
So if you intend to keep the FC higher and not let it fall, because of your higher CYA level, then yes you should add some acid to lower it. You could wait for your FC to drop to 10 ppm or so before checking the pH again and then adding acid just to play it safe, but I see nothing inconsistent in your numbers.

Again, hypochlorite sources of chlorine DO raise the pH upon addition. They are only close to pH neutral when the added chlorine is consumed/used. This means that ongoing use of such chlorine doesn't keep having the pH go up and up, at least not quickly (there is a small amount of excess lye in chlorinating liquid and bleach). However, in your situation, you are raising the FC fairly permanently so the rise in pH from your chlorine addition will also be fairly permanent and therefore needs adjustment by adding acid to lower the pH.
Chem geek's above example was for an FC rise of 12ppm, the rise would higher if more chlorine was added.

I do believe that this effect is real, and should be kept in mind especially when going to slam level for higher CYA-levels, and that chem geek's PoolEquations.xls spreadsheet will give a good estimation. It doesn't use simple analytical formulas, but scripts to find the chemical equilibrium in an iterative process. I assume that this will still utilize certain approximations that will have more influence the further away you are from "normal" water parameters, but the trends should still be valid. At very high CYA, TFP recommends to drain the pool first to lower CYA before starting to slam. This will not only reduce the required slam FC to a manageable level, but will also ensure that pH doesn't get far too high during the slam.
 
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