pH rise with SWG

[Derb22]

Love this discussion, as I completed the SWG conversion this year. For my pool I am adding 1/2 gallon of acid per week. I am slowly lowering my TA after getting it to 70 shortly after adding both salt and borates. I plan on lowering TA to 50 to see if this will stabilize PH. As it stands it doesn’t really matter what I lower the PH to as it will take about the same amount of time to creep back to 8.0. I do have a question, if I add two drops of acid demand to the PH test and that drops it to 7.6. Does that give me an equation to know what the PH accurately was? 1 drop? I’m tempted to leave the pool alone and see where it might stabilize if I had a way to know exactly how highover 8.0 the ph was.

 

[NYY]

While we're on the subject of SWG PH and talking of changing some of the statements, I think the below needs to be corrected from the SWG pros and cons page. Everyone, and I say everyone I know with a sandstone or limestone coping and/or pavers has very noticeable exfoliation on a regular basis. In fact, even when I meet strangers, and we get on the subject of our pools, as soon as I hear about their exfoliation, I ask if they have an SWG and it's always yes. In fact, the problems may seem rare b/c the people think it's normal with this type of stone (from many interviews). 9 years with my Oklahoma flagstone coping and not 1 millimeter of an area has exfoliated (no SWG). I would like to see the last sentence below eliminated. And somewhat to the point of the OP, I do believe there's an issue with SWG and PH issues not seen with bleach.

"The two most common situations where damage has occurred are in indoor pools, where the FC level has been allowed to get way too high, and when you have one of the softer kinds of natural stone (sandstone, limestone, etc) above the water line, and the stone gets splashed regularly, for example in a waterfall. Even in these two situations, problems are rare."

 

[kicksavedave]

Great thread, and while I don't have much to add beside my own personal obvservations, they may be applicable (or may not, you decide).

I have a newly redone pebble pool, opened in late April. After that first month, running the pump on 1500 RPM 24x7, I turned on the SWG and got my FC to around 5 after some tinkering with the SWG percentage, which was around 20%. 25 seemed to make it climb, 15 seemed to keep it steady around 3 or 4, so 20% seemed right. But with a pool cover on most of the time, except when swimming, with CYA of 60 my FC loss was almost nothing. The PH would rise rise constantly, about .1 per day. Every 4 days I'd throw a gallon of MA in there, drop the PH by .4 (usually from 7.8 to 7.4) and the TA would also fluctuate between 80-90 with each PH rise and MA dose. I went away for 10 days and despite having a "pool guy" check it and add MA for me in the middle, I returned to 8.1, so two gallons of MA go in, down to 7.2, and the rise begins again. I just assumed my PH rise was because it was a new pebble finish and I did wonder if it would stop eventually. Then I read some threads on TFP showing its a normal side effect of having a SWG. Oh ok, I stocked up on MA to deal with what I thought was just my pools normal acid demand. Also, with the cover, and thus almost no evaporation, I'm barely replacing any fill water at all. My water bill confirms this, undetectable difference to prior to filling the pool. Autofil dribbles just a trickle, occasionally, usually after a swim but its a tiny amount.

But then I started considering solar electric, and that means changing electric plans to "Time of Use" and 4PM to 9PM is peak time. So to prepare I stopped running the pump 24x7 @ 1500 and 20% SWG, and started running it 18 hours 15.5 hours per day at 1650 RPM and 30% SWG. Well my FC shot up to 10, so that was too high on the SWG. But I also noticed that at the same time, my PH rise basically went to zero. I added one gallon of MA the day I made the change to drop from PH 7.8 to 7.4, and its at 7.5 since then for well over a week, including running a fountain for the past two days to cool the pool down. I lowered the SWG to 5% to let my FC drop back down to 5, and it dropped to 3 so I went back to 10% and we'll see where that gets me. My point of all this is that changing the time and the % on my SWG is the only real big change I made and my PH rise has basically stopped.

My hypothosis after reading this thread is this. Water running through an SWG at various speeds should produce various levels of bubbles. Like with propellers on boats, there should be a theoretical number where there is the least cavitation, the most efficient passing of the water through the SWG, which creates the least amount of bubbles. This -may- explain why some people, even in this thread, experience different results simply by turning on their SWG, and others experience no change. Perhaps adjusting the run time and pump speed and % output of the SWG, one could find an ideal setting where the bubbles produced do not contribute to any PH rise and the rest of the chemisty takes over?

Or maybe I'm entirely full of baloney in which case feel free to tell me so All I know is, I tinkered with my run time, pump speed and % and my PH rise instantly stopped. Now what do I do with all this extra MA I have on hand?

 

[Dirk]

Interesting hypothesis, kicksavedave. But I don't think the hydrogen bubbles are being produced by cavitation or motion or flow. I believe it is only a chemical reaction (someone will correct me if I'm wrong about that).

I think of it this way... (My own layman's interpretation/explanation) The SWG creates chlorine using electrolysis: the salt water acts as a conductor between the two sets of plates in the SWG, making the electrolysis possible. The bubbles (hydrogen) are a byproduct of the chlorine producing process. The creation of chlorine, and therefore the hydrogen bubbles, is not affected by flow. The only reason there is a minimum flow requirement at all, is to be sure there is an adequate supply of salt, and the chlorine gets carried away from the SWG into the pool without incident. The flow is the transport system, not part of the production system. The same amount of chlorine and hydrogen bubbles is created regardless of the speed of the water passing by the plates. Imagine two electrodes, and a long metal bar completing a circuit between them. Say the bar has some resistance. The amps running through the bar would create heat. The current flowing between the two electrodes, and the heat, would be the same if the bar was stationary, or being physically slid through the electrodes. The speed at which the bar was slid would not affect the amps or the heat generated. The water is acting like that bar, the hydrogen is like the heat by product. The plates are creating the chlorine from the salt, regardless if it's moving or standing still. As long as there is an adequate supply of salt, the chlorine happens. The bubbles happen. The plates can only utilize X amount of salt, pushing less or more past the plates won't make more chlorine, more hydrogen, or more bubbles (as long as the necessary salt is present). I think!

So that's my guess as to why changing flow rate or runtime would not affect pH. At least not for the reason you're thinking.

Thoughts?

There is excellent science here that "proves" an SWG doesn't affect pH. And yet it does in some pools. Is this like a bees ability to fly? For years science could not explain why a bee could fly. And then scientists figured it out. I may be misunderstanding and/or perpetuating the bee myth, so that might not be a proper example, but the point is, there are things that exist that have yet to be explained. Is this SWG-pH phenomenon one of them?

 

[cowboycasey]

flip side of this ( I know you have a gunite pool so not the same ), I have had a SWG for 4 years, I have not added any Muriatic Acid for a year, my PH has been at 7.5/6 since July 17.... My TA is low and my CSI is low but I have a vinyl pool so no issues...

 

[Spa Owner]

There is excellent science here that "proves" an SWG doesn't affect pH.

The most common misunderstanding is SWG produce chlorine. More technically sodium based chlorine as the salt is sodium chloride. Logically this suggests the output would be a form of sodium hypochlorite. Logic again suggests the pH of the sodium hypochlorite produced would be the same as that we buy in a bottle at the store.

Unfortunately this logic is false. The salt chlorinator may produce some NaOCL. However it is not all that, nor is it all hypochlorous acid and other derivatives. Like all things water every thing is equally true. The other factor is the nature of water which will effectively be combining and disassociating ions on an ongoing and constant basis.

The pools reporting rising pH will invariably have higher levels of buffer in some form. Even phosphates can act as a buffer, and it is difficult to provide a more exact understanding of why one pool acts a certain way and another; another without substantially more information.

What is a scientific fact is the pools contain dissolved carbon dioxide. This is not at equilibrium with atmosphere. The gas strives to reach equilibrium with atmosphere (close enough for discussion) and in doing so lifts the pH. Lowering the content of

dissolved carbon dioxide will result in more stable pH. This is not an opinion. This is a simplified explanation of the science.
​

 

[kicksavedave]

Interesting hypothesis, kicksavedave. But I don't think the hydrogen bubbles are being produced by cavitation or motion or flow. I believe it is only a chemical reaction (someone will correct me if I'm wrong about that).


So that's my guess as to why changing flow rate or runtime would not affect pH. At least not for the reason you're thinking.

Thoughts?

There is excellent science here that "proves" an SWG doesn't affect pH. And yet it does in some pools.

Well, for me the chemists here who make the scientific case that a SWG doesn't impact PH make a well thought out case and it sounds right to me. But then I saw with my own eyes how tinkering with my SWG run time and % output coinsided with a noticable drop in PH rise. My only other explanation for that is that my newer pebble pool stopped curing and releasing gasses that increase PH, but that seems like it shouldn't have been a sudden event. One last possible explanation is the heat wave that brought my pool to 97/98 degrees during the peak of the afternoon on several days. Finally I'm wondering how my pool cover being on most of the time affects my PH?

Regardless, thanks to TFP, I'm going to continue to work to get my chemistry ideal for stable PH, and then dump all my excess MA on the banana palms that just won't die

 

[Dirk]

Regardless, thanks to TFP, I'm going to continue to work to get my chemistry ideal for stable PH...

Absolutely! With the ability to test and dose ourselves, learned here, we know what our pools our doing and how to make the needed adjustments, even if we don't know or understand the why of it...

 

[JoyfulNoise]

I would like to please urge everyone to use the Search box more and post less. 99% of what is being discussed here has been discussed, at great length, in the past. If you use the search box, you will find past threads with very definitive answers in them.

I can’t possibly correct every wrong assertion here, but let me make a few points -

1. SWG’s do not cause stone work degradation. Anectdote is not data and correlation is not causality. There are many threads discussing why Texas has problems with stonework and SWGs and why Texas pool builders have been pulling away from SWG pools over the past few years. 99% of the time it is due to pool owner chemical negligence and/or poor choice of stone materials used around the pool. The SWG is not the cause.

2. Flow rate through the SWG makes no difference in the amount of hydrogen gas evolved and thus will have little to no impact on aeration. The amount of H2 gas created is fixed exactly by the amount of chlorine produced. Thus, if the creation of the hydrogen gas bubbles has any effect on absorbing CO2 from the water, flow rate is going to have nothing to do with it. Cavitation is not typically possible in pool plumbing as the pump would have to be operating far off of it’s pumping curve with very high flow rates. If cavitation were present for any length of time in the plumbing system, physical damage to the cell would happen.

3. SWG’s produce chlorine gas, FULL STOP. That is why they are coated with an expensive transitions metal oxide catalyst - so that the only reaction favored is the production of chlorine gas. They do not create bleach and the counter ion (sodium) is irrelevant to the reaction. You could just as easily use potassium chloride in your pool and you would get exactly the same effect (assuming you added enough KCl to ensure the chloride ion concentration is correct). When the SWG plate creates chlorine gas, the chlorine gas dissolves in the pool water and several things happen to the chlorine - the chlorine gas forms 1 mole of chloride ion (Cl-) and 1 mole of hypochlorite ion (Cl+). The hypochlorite ions then almost instantly form one of three different active chlorine compounds - they can combine with cyanurate to form a stabilized chlorinated cyanurate ion or they will form either hypochlorous acid (HOCl) or hypochlorite ion (OCl-). 95% of the sanitizing chlorine that forms (Cl+) binds to cyanurate and is held in reserve. The remaining 5% or so will split up between HOCl/OCl- depending on pH. Any OH- created in the process of the Cl2 gas dissociating will eventually get used up as the sanitizing chlorine reacts. So, in the case of the SWG, all hydronium (H3O+) and hydroxide (OH-) is conserved. Therefore, no change in pH will ultimately occur.

4. Bleach is only caustic because the hypochlorite manufacturing process creates it AND sodium hypochlorite is only stable at high pH (pH > 12). So excess caustic is added to bleach to stabilize it against decomposition. All metal ions (including sodium ions) catalyze the decomposition of hypochlorite and so high pH is an absolutely necessity.

Again, none of this new and all of it can be found with a few simple search queries.

 

[PoolStored]

flip side of this ( I know you have a gunite pool so not the same ), I have had a SWG for 4 years, I have not added any Muriatic Acid for a year, my PH has been at 7.5/6 since July 17.... My TA is low and my CSI is low but I have a vinyl pool so no issues...

@cowboycasey Tried looking for your logs, no joy.

How low is your TA and what does your CSI run?

Will start a new SWG in the spring. New liner going in this month. Want to prep the water and get TA down before I start...need a target.

 

[Newdude]

Want to prep the water and get TA down before I start...need a target

As long as it’s 100 or less it will usually find its own sweet spot as you manage the PH. (Sometimes even 110).

If you’d sleep better speeding that process up, (you are kinda ‘extra’ and all, and I mean that as a compliment ), target something mid range, say and 80, and then either way it wants to go on its own should be relatively quick.

 

[PoolStored]

As long as it’s 100 or less it will usually find its own sweet spot as you manage the PH. (Sometimes even 110).

Got it.

(you are kinda ‘extra’ and all, and I mean that as a compliment ),

Are you saying you want to be my friend?

target something mid range, say and 80, and then either way it wants to go on its own should be relatively quick.

All I know is that with LC and borates. My pool started the summer (June 1) at 7.4 and 70. As it sits now, end of September it is 7.6 and 80. Not a lick of MA has entered my pool since SLAM. If 30,40,50 would keep the MA at bay with SWG, I have a lot of MA and a kick Rear aerator that I can drive TA that low before I fire SWG up in the spring. Trying to get a data point from @cowboycasey who seems to have a formula for his pool, also vinyl.

 

[Catanzaro]

Pools are funny! I had years where my PH was over 75-80 and had constant PH Rise. This year, it was at 100-110 with no rise. However, I reduced the circulator rotating heads (used 3 instead of 4) so maybe this made the difference. Gunite pools I would suggest low PH and borates if you have constant rising PH issues. Shut off waterfall, and any other things that cause PH rise.

 

[cowboycasey]

Hey there, just got the notification

My CSI is between -0.30 and -0.40 depending on the season.. right now it is -0.33.. I try to keep TA at 70 to 80 ish, Ph stays stable way longer now that I have Borates.. I had a Borate situation and crashed my PH and TA and had to do emergency procedures.. That was a fun day... everything is stable now but I spent a month dropping my TA and PH..

Just a warning > When adding Boric Acid do not add the Muriatic Acid recommended when using 20 Mule Team Borax

 

[PoolStored]

Just a warning > When adding Boric Acid do not add the Muriatic Acid recommended when using 20 Mule Team Borax

Not sure I understand this statement.

 

[cowboycasey]

Not sure I understand this statement.

Well, you see.. I missed the part where you only add Muriatic acid when using 20 Mule Team Borax.. I thought you also add acid when you use Boric acid and you do not...

So I had everything perfectly balanced, added the Boric Acid then added the Muriatic acid.. checked PH and it went of the charts low and checked TA and it was 0... shut the pump off, went to the store and got baking soda and washing powder..

I will say when I get my all tile pool done I may have a harder time with PH rise as I will need to raise CH and I am not sure if I want to keep my CSI at -0.30 all the time.. I think it will be fine with the borates added.. I really will not know until I get it done..

 

[JoyfulNoise]

Not sure I understand this statement.

You can add borates to your pool water by one of two means - either you add borax (sodium tetraborate decahydrate) OR you add boric acid. Borax is a strong base and will raise pH very quickly so you must add a corresponding amount of acid (muriatic acid) to keep the pH stable. 1 mol of borax requires 2 mols of acid to keep the pH stable. Boric acid, by contrast, is a weak acid and so you can add it directly to your pool and the pH will change very little (about 0.3 units for every 50ppm B you add). Most people find adding boric acid much easier (just don't do what @cowboycasey did ... or else you'll need to buy a change of underwear with the baking soda and washing soda needed to rebalance the water).

 

[cowboycasey]

Trust me, the checkout lady looked at me like I was crazzy buying that much washing powder and baking soda.. The funny thing is there was so much dust on the boxes I am sure they were happy someone finally bought it

 

[JoyfulNoise]

Trust me, the checkout lady looked at me like I was crazzy buying that much washing powder and baking soda.. The funny thing is there was so much dust on the boxes I am sure they were happy someone finally bought it

Costco sell A&H baking soda in 13lb bags so you can look normal and say to the checkout cashier, “I just really, really, really have A LOT of cupcakes to bake!!!”

 

[PoolStored]

Trust me, the checkout lady looked at me like I was crazzy buying that much

The look when I bought all the bleach that Aldi had for my SLAM...she said, "I'm not going to ask..."