Turning the SWG off during SLAM

mgtfp

Bronze Supporter
Mar 5, 2020
301
Melbourne, Australia
I just started replying in a featured thread (Featured - How do i know if i'm generating Chlorine?), but then thought that this would go too much off-topic for the OP, and decided to start a new thread here instead. Background is the question if the SWG should be turned off during a SLAM or not. This seems to create some confusion in multiple threads, I have been reading.

I know that the Pool School mentions in the SLAM description to turn off the SWG for the duration of the SLAM. But I have also read somewhere on TFP that once you have reached shock level by adding bleach, you can use the SWG to support maintaining shock level. I can't remember if that was an older version of the Pool School article, or a different thread. I see reasons on both sides.

Pro:
  • By running the SWG you give the SLAM an extra boost by benefiting from the locally increased chlorine concentration within the SWG cell.
  • By running the SWG during daylight hours for lets say 10 hours a day on 100% you would create, in the example of the above linked featured thread, 3.2ppm of chlorine. Not enough to maintain shock level during a SLAM, but it's (for the pool size in that thread) nearly half a gallon of high strength bleach per day that doesn't need to schlepped home.
Con:
  • You never know exactly how much chlorine your SWG is producing, depending on water temperature, salt level, calcium deposits on the electrodes, age of the cell. That makes it more difficult to judge how much chlorine has been eaten by algae and how much bleach to add to maintain shock level.
  • Running the normal, scheduled, SWG cycles that might reach into the non-daylight hours (running too long in the afternoon/evening or starting too early in the morning), you can stuff up the validity of an OCLT.
  • Increased risk for calcium scaling in the cell. pH will rise due to the addition of bleach (or creating chlorine by running the SWG). Even though this part of the pH-rise is only temporary and will eventually get compensated by the different ways that chlorine levels get reduced, during the SLAM (especially on higher CYA levels that will require addition of more bleach) there will be times of higher pH (which we are blind for while at high FC), that can create, together with increased temperatures within a cell running at 100%, a critical CSI.
  • Due to the hydrogen bubbles created by the SWG, there will be more CO2 out-gassing, leading to a faster pH rise during the SLAM. And this part of the pH-rise won't get compensated by chlorine being used.
I tend to think that the con reasons outweigh the pro reasons. What is the experts' opinion on that? Have I missed any arguments?

Cheers,
mgtfp
 
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YippeeSkippy

Mod Squad
LifeTime Supporter
Jan 17, 2012
13,901
Evans, Georgia
Another Con: More wear and tear on the cell, possibly/likely shortening its lifespan if done often. I'm stingy with use of my cell unnecessarily, which allowed me to keep one 9 yrs.

I personally would leave mine off if I had to do a SLAM process as using the liquid chlorine only with dosing gives you a better idea of how much its still getting chewed up by algae.

Maddie
 
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mgtfp

Bronze Supporter
Mar 5, 2020
301
Melbourne, Australia
That's a good one, Maddie.

I don't exactly know how old my cell is. I know from the records the previous house owner gave me, that the SWG was installed in 2005. And talking to the pool shop that installed the unit, the cell seems to have been replaced once. Certainly haven't replaced it on the four years I am living here, and the cell didn't look new when we moved in. Quite happy with that. I am getting more nervous now that the electronics of the main unit might be failing while away on holidays. But the cell still seems to be going strong. Certainly worth looking after it by not putting it under unnecessary stress. And giving it a well deserved ma bath from time to time to remove calcium deposits.
 

Newdude

Well-known member
Jun 16, 2019
3,827
NY
The primary raeson to shut off the SWG to SLAM is to have one level set of instructions for all pools worldwide. There are different manufacturers with different outputs that respond differently in certain climates. Bleach responds the same everytime everywhere and the strength% is printed on the bottle.

The depreciation in cell life is often less than the cost of the bleach used to SLAM, but many folks prefer to stretch the cell life every second they can, even if it's counterproductive.
 

calinb

Well-known member
Jul 18, 2018
116
N. Central, ID
Another Con: More wear and tear on the cell, possibly/likely shortening its lifespan if done often. I'm stingy with use of my cell unnecessarily, which allowed me to keep one 9 yrs.

I personally would leave mine off if I had to do a SLAM process as using the liquid chlorine only with dosing gives you a better idea of how much its still getting chewed up by algae.

Maddie
Your second point is the one that matters to me, though I can always turn it off when I feel I'm ready to do a OCLT. Wear and tear though? Yup--it costs ya' (and electricity too) but, according to my calculations, bleach costs more--especially during these panic-demic times!
 

mguzzy

Gold Supporter
Jul 8, 2015
2,051
OV, CA
This is a good question to post to it's own thread. The first reason in your list of cons is what I think is most important. Often when doing a SLaM it's important to know what the chlorine demand is. Even before one gets to the OCLT stage of the SLAM. And it's near impossible to know that if you have multiple sources of chlorine adding FC to the water.
@Newdude makes an excellent point too about making the instructions more universal as well when we are trying to explain the process to newbies.
That said, the pros have some validity, shall we call that advanced techniques for experienced SLAMmers. But if you have lots of experience slamming your pool, some how you have fallen off the TFP bandwagon.😉
 
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calinb

Well-known member
Jul 18, 2018
116
N. Central, ID
This is a good question to post to it's own thread. The first reason in your list of cons is what I think is most important. Often when doing a SLaM it's important to know what the chlorine demand is. Even before one gets to the OCLT stage of the SLAM. And it's near impossible to know that if you have multiple sources of chlorine adding FC to the water.
Until I'm ready to do an OCLT, I only need to now if I'm adding Cl fast enough to keep up with demand and maintain the target SLAM level. Even if I'm adding some or all of the Cl with my SWG, I can tell if I'm keeping up with demand and that's all I need to know. In fact, continued testing, even while running the SWG, will tell me when I've "turned the corner" on the treatment and demand starts to drop. That will tell me that I should consider turning off the SWG soon and doing an OCLT.
@Newdude makes an excellent point too about making the instructions more universal as well when we are trying to explain the process to newbies.
That said, the pros have some validity, shall we call that advanced techniques for experienced SLAMmers. But if you have lots of experience slamming your pool, some how you have fallen off the TFP bandwagon.😉
I've had to SLAM three times--once when I first got the pool with the house and opened to a swamp with a dead pump and now twice this year, which I believe were due to the inaccuracies and difficulties of obtaining correct TC, FC, and CC values using either OTO or FAS-DPD tests for weeks (and even months) after a Jack's #2 /sulfamic acid treatment. After doing the treatment late last fall, I opened to a green pool this spring. That didn't happen before and I blame it on the residual Cl ALL being bound, due to the Jack's sulfamic acid stain treatment. Even now, six months later, nearly half of my Cl is still bound, but that's better than where I started (all of it bound and reported as CC)! I don't think the Cl bound by the sulfamic acid is terribly effective as a sanitizer. The good news is my copper stains have not come back, even with the two SLAMs. Was the stain treatment worth it. I don't know. Stains start to look like modern art on the pool Gunite after buying pounds and pounds of chlorine--SWG or otherwise and closing the pool for SLAMs!
 
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mgtfp

Bronze Supporter
Mar 5, 2020
301
Melbourne, Australia
I also think that @Newdude 's point of universal instructions is very valid. I guess, as long as you understand what you are doing, you are fine either way.

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.

In hindsight, I think this is what happened to me in my first SLAM. I have quite an old SWG that can't be turned to 0%, and it is very fiddly to unplug the pump from the SWG and plug it straight into a powerpoint (the real fiddly bit is actually getting the plug back into the SWG, because you can't see the SWG's internal powerpoint for the pump, so you have to get the unit off the wall). Initially, I actually thought that the pump was hard wired into the SWG. So, when I did my first SLAM, I just turned my SWG down to the lowest setting and started adding chlorine (I actually used cal-hypo, as my fill water is very low in calcium and we get a fair bit of rain over winter, I have to increase CH from time to time anyway).

SLAM itself worked fine, but shortly after that, I started to get calcium flakes accumulating in front of the water returns. At the time, I was puzzled, because CSI after the SLAM was always in the range between -0.3 and -0.05. But later I understood that during the SLAM I must have had a very positive CSI and the cell was running. Using cal-hypo probably made it even worse, because I might have had local patches of higher CH-levels that went through the cell. Calcium flakes that came off the cell must have accumulated in the pipes and kept blowing out of the returns for weeks.

Now, I do re-plug my pump into a powerpoint if required. But that process alone is actually one of the reasons why I am considering to upgrade my SWG. Next to always having a bad feeling when going on holidays that my old SWG might fail.

Most people won't know that adding bleach or cal-hypo will temporarily increase the pH (I didn't...), because in normal operational modes it doesn't matter, once the chlorine gets used or "killed" by UV, that initial rise get's compensated, it's just part of your normal pH-cycles. And the pH-rise by small additions to stay at target-FC won't even create a significant colour change in the pH test. I guess, that's why the pH-rise is not shown in the effects-section of PoolMath. But it was quite an eye-opener when I started to get familiar with chem geek's Poolequations.xls.

That shows how important Newdude's point of universal instructions is: Turn the SWG off - and make sure you get pH down to 7.2 before starting to SLAM. Unless you understand the potential consequences and know how to deal with them, and the points on the pro-list are important to you.
 

nlindelldc

LifeTime Supporter
Mar 21, 2015
429
South Texas
I think perhaps you are overthinking it. I run my SWG during a SLAM to maintain my FC levels above Shock level. Why have to add bleach every day, isn't that what you bought the SWG for in the first place?
 

mguzzy

Gold Supporter
Jul 8, 2015
2,051
OV, CA
I think perhaps you are overthinking it. I run my SWG during a SLAM to maintain my FC levels above Shock level. Why have to add bleach every day, isn't that what you bought the SWG for in the first place?
You are absolutely right.. but if you need to chart what your chlorine demand is, its hard to do when there is more than one source of chlorine addition.
 
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Flying Tivo

Well-known member
Jan 24, 2017
1,799
Monterrey, NL, Mexico
The main point has been made, you dont know how much FC the Slam will consume, it could be organics or ammonia. One consumes more than the other. So in the grand scheme of things, the SWG is only providing less than 10%(wild guess) of the FC required. So why waste cell life.
 

calinb

Well-known member
Jul 18, 2018
116
N. Central, ID
I could see that
For a SLAM, I don't think that precisely quantifying chlorine demand really matters much, except at night when you elect to do an OCLT (and then your turn-off the SWG and eliminate all other sources too). During a SLAM, you must only keep up with demand but I don't see any reason to precisely chart it. As demand falls, you'll be dialing down the timer (or manually adjusting) run time on your SWG and/or reducing other Cl sources. When the demand seems to be about normal, you'll do an OCLT, regardless of whether you adjust demand with SWG run time or LC jug quantities.

I had my SWG up and running for my last SLAM (before I got my post-Jack's #2 stain treatment water fully rebalanced from last year's treatment and, I believe, more prone to suffering algae using just TC readings imposed by the #2 treatment). My SWG produced up to about 10 ppm Cl per day in my pool and saved me money over jugs of LC. I kicked off the SLAM with calcium chloride granular shock, because I wanted more CH, and then I left the SWG to run at 100% for the night before confirming a SLAM level of chlorine in the morning.

You might think a SLAM unnecessarily wears out an SWG cell, but keep in mind when assessing the economic costs that you'll be turning off the SWG for, very likely, a few days after the pool passes an OCLT in order to return to normal FC levels--just as you'd eliminate LC additions too.

LC has become too expensive around here and it's the reason that I bought an SWG this season. Economically, it pencils out for me to use it as much as possible during a SLAM as well as for normal maintenance.
 
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mgtfp

Bronze Supporter
Mar 5, 2020
301
Melbourne, Australia
Valid reasons, Cal. I thought the same, when I slammed a couple of months ago. But I did have lots and lots of ca flakes coming out of the returns for a while after the slam. Never had that before, and never since. I have very soft fill water, low in CH and TA.

I underestimated the initial pH rise after adding adding chlorine to get up to shock levels (see example in my earlier post - and my parameter were worse, see below). My pH was 7.4 before adding chlorine and my TA also was still in the pool store recommended range, which probably added to the problem. That was still in my transition time to TFP.

Now I understand the chemistry in my pool a lot better. Before slamming again, I'd run a complete test to get a current CSI, and would be able to predict how it changed during the slam with the TFP tools. I'd also definitely lower the pH down to 7.2 first and not think that 7.4 is good enough. You learn from your mistakes...

As long as people know what they are doing, having SWG support during a slam can be beneficial. But you need to be aware of higher CSI when getting up to slam-FC and maintaining it. pH will only get down to normal again with sinking FC when the chlorination cycle gets closed. And you need to be aware that adding chlorine from multiple sources will make it more difficult to estimate your chlorine losses, especially via remote TFP-forum support.

I think for a general guideline, that leads to success in most circumstances, keeping the SWG off is the safer option. And it will be a lot more likely that all relevant information gets to the TFP-guides talking new members through their first slam. 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?

Most people seek help here with pools still on pool store levels, and no experience yet with the TFP method. The first aid guidelines need to be simple and as standardized as possible. Just as they are...
 
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Newdude

Well-known member
Jun 16, 2019
3,827
NY
Most people seek help here with pools still on pool store levels, and no experience yet with the TFP method. The first aid guidelines need to be simple and as standardized as possible. Just as they are
^^^^. Right there. New and confused members need to learn how to care for their pool. Having the SWG assist in any way will only take away from the knowledge that will keep them clear going forward. Without that knowledge, or with only half of it, it will only be a matter of time until they are back at square one.

Rest assured it will be TFPs fault and not their own. So we shut down the SWG. Give the newb a crash course in doing it the hard way. They learn, it works, and they sing our praises with undisputed results.
 
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mguzzy

Gold Supporter
Jul 8, 2015
2,051
OV, CA
@mgtfp You nailed it on the head MG... (hey another MG*)... If you know what the effects are of running your SWG during a SLAM then by all means do it. The point is educating pool owners so they know thier own pitfalls and promises of doing things a certain way. For the first time newbie.. it's likely TMI and yet another unknown ball to juggle.. so turn it off. Then use your SWG in next SLAM... if you have one.
 
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