SWCG doesn’t drive Ph up?

[cwswifty]

I’ve read quite a bit in the forum about this topic but what Im seeing doesn’t seem to align . I’ll assume I’m looking at this incorrectly and look forward to getting smarter on the subject. Also, full disclosure, my pool experience began last October so I am definitely not an expert.

For the last couple of months, since the pool has been below 54 F, I’ve been maintaining FC levels with liquids chlorine. My TA has been 70 and I’ll let PH go to 8.0 before adjusting. It would seem to hover in the high 7’s for over a week before needing any MA to bring it back to 7.6.

Now that my pool temp is in the high 50’s and lower 60’s, I’ve raised my salt levels to 3200 ppm and put the SWCG to work. Only needing to run it between 10% and 20% to maintain proper FC levels. CYA is at 50 ppm for now. Now that the SWCG is on the job my PH rises much quicker from 7.8 one day to 8+ the next. Yes I have a spa spillover and tanning ledge bubblers that run for 5 mins per day to circulate the chlorine. That has been a constant thought, nothing new. The only thing that has changed recently is the use of the SWCG. Am I to believe that the SWCG is not responsible for my rapidly rising PH?

 

[mknauss]

SWCG do not substantially effect pH. They can have minor effect, but that is normally overwhelmed by other factors, especially high TA fill water added due to evaporation.

 

[Divin Dave]

The only thing that has changed recently is the use of the SWCG. Am I to believe that the SWCG is not responsible for my rapidly rising PH?

Don't rule the SWG out for being at least partly responsible for pH rise.

Running your SWG at 10-20% might make the pH rise, it really depends on the RUN TIME. How SWGs work.... The SWG will produce chlorine at full power for 10-20% of the time it's running.

For example, In my case I run my VSP 100% of the time, so for me, a 20% on the SWG is 4.8 hours generating chlorine. My cell is size for 30K gallons, so that's a good bit of very tiny bubbles being pumped into the pool.

Pure chlorine is a gas being generated by the SWG, and so the water going to the pool is filled with millions of very tiny bubbles. When it gets into the pool, the bubbles rise to the top and out-gas CO2, and the outgassing can make your pH rise. The bubbles are so tiny, that people may not even be able to see them when they get to top of the water. But they are there.

Some folks struggle with SWG's and pH and others not so much. It's largely due to what type of pool surface you have and the TA. I keep my TA around 50 and don't have any problem with pH rising, but if I go 70 or above, I have to adjust pH a lot more often.

Its largely a matter of trial and error exercise to find the sweet spot and get the thing to settle down and behave.

 

[cwswifty]

@mknauss:
I hear you. My fill water was measured at a TA of 20. The only things that I can think of that have recently changed are temperatures above 54 F and the SWCG being put into use. All other things, as far as I know, have been consistent.

 

[cwswifty]

Don't rule the SWG out.

Running your SWG at 10-20% might make the pH rise, it really depends on the RUN TIME. How SWGs work.... The SWG will produce chlorine at full power for 10-20% of the time it's running.

For example, In my case I run my VSP 100% of the time, so for me, a 20% on the SWG is 4.8 hours generating chlorine. My cell is size for 30K gallons, so that's a good bit of very bubbles being pumped into the pool.

Pure chlorine is a gas being generated by the SWG, and so the water going to the pool is filled with a lot of very tiny bubbles. When it gets into the pool, the bubbles rise to the top and out-gas CO2, and the outgassing can make your pH rise. The bubbles are so tiny, that people may not even be able to see them when they get to top of the water.

Some folks struggle with SWG's and pH and others like me not so much. It's largely due to what type of pool surface you have and the TA. I keep my TA around 50 and don't have any problem with pH rising, but if I go 70 or above, I have to adjust pH a lot more often.

Its largely a matter of trial and error exercise to get the thing to settle down and behave.

Perhaps I should try lowering my TA from 70 to 50. I’ve considered this after reading here, but I wanted to check with the experts one more time.

 

[JoyfulNoise]

When was your pool plastered?

 

[Divin Dave]

Perhaps I should try lowering my TA from 70 to 50. I’ve considered this after reading here, but I wanted to check with the experts one more time.

EDIT - See Joyful Nose Question. If our plaster is less than a year old, then the normal TFP rules do not necessarily apply.

It wont hurt to do that. If it were me, that's what I would do.

Just as a thought for you regarding your overall pool chemistry...
lowering the TA will make your CSI go in the negative direction but if you only go 20, it will not move by very much. If CSI is of any concern to you, increasing the CH will make the CSI go back where it came from. BUT DON'T add any CH until you find the sweet spot for your TA and pH. After you find the sweet spot is when to add any CH. If your Fill Water is high in CH, then you might not want to actally add any CH at all other than by your fill water.

Also as the water warms up, it will also make your CSI go more Positive.
Having said all of this, my advice is don't worry too much about CSI until the water gets well into the 70s. You can drive yourself crazy trying to chase it early in the springtime.

 

[Divin Dave]

When was your pool plastered?

Matt makes a very valid point. Plaster that is less than 1 year old need special attention.

 

[mgtfp]

The chlorine gas will dissolve into the water before the rechlorinated water reaches the water surface. It's the hydrogen gas that gets created at the cathode that doesn't dissolve and bubbles out at the pool return. These bubbles don't contain any CO2 (since being hydrogen gas bubbles), so dissolved CO2 in the water finds (additionally to the air above the pool) another volume that's in contact with the water where it can outgas into, faster than CO2 from the gas volume can dissolve back into the water.

Potentially, a SWG can therefore contribute to pH-rise. The extend of that effect is debatable.

Should chlorine gas really not dissolve and bubble out at the return, you'd have another effect that would have a much bigger impact on pH than potential CO2 outgassing into the chlorine bubbles: The production of hydrogen gas comes with production of hydroxide, which initially raises pH. This rise gets eventually compensated by chlorine (dissolved into the water as HOCl, OCl^- and chlorinated cyanurate) being "used" by killing stuff and being lost to UV. If some chlorine outgasses straight away, it will eventually miss to compensate the initial pH-rise.

This effect would also come with a TA-rise.

General consensus is that the generated chlorine dissolves pretty much 100% into the water. It would require a very short return line for that effect to become noticeable.

 

[cwswifty]

When was your pool plastered?

October 2023.

 

[cwswifty]

Is it plausible with 5 month old plaster that when I sanitize with liquid chlorine the Ph doesn’t need MA for 7+ days but when a SWCG provides the chlorine it needs MA in 2 or 3 days?

 

[mknauss]

Water temperature has a significant effect on carbon dioxide out gassing

 

[cwswifty]

Water temperature has a significant effect on carbon dioxide out gassing

Ok I’ll try to search on the relationship between water temp and CO2 out gassing. In general, are you saying there may not be such a PH affecting difference between liquid chlorine and a SWCG once the water warms up? Hopefully that is the case. I’ll be glad to use liquid chlorine until the water warms a bit more. Just trying to understand.

 

[mknauss]

I suspect the curing of your plaster is more active when the water temperature warms.

Anecdotally -- a moderator here has a Fiberglass pool in metro Atlanta area. She has a SWCG with low TA fill water. Her pH is steady. Never changes. No acid. With SWCG use.
I have a fiberglass pool. During the winter and early spring, I am running my SWCG but have little need to add high TA fill water (less evaporation and occasional rainfall). My pH rises very slowly during that time. Once evaporation kicks in, and I am adding high TA fill water, my pH rises and I add acid twice a week to keep the TA under control.

 

[JoyfulNoise]

There’s a couple of issues that should be considered -

1. You can not compare cold water conditions and warm water conditions easily. Temperature affects a lot of variables and warm water out gases faster than cold water. So your pH rise is going to be seasonal no matter what.

2. Your new plaster could still be emitting some caustic compounds. That will pH rise a continuous issue until the plaster ages.

3. You need to be careful with such low TA fill water and always ensure that your CSI is balanced or only very slightly negative. Cold water is more aggressive towards plaster than warm water and new plaster needs proper calcium saturation or else the water will actually strip the plaster of more caustic calcium compounds thereby causing the pH to rise. TFP has seen this before with newly plastered pools being allowed to sit over winter with aggressive water and then the pool owner opens the pool to find the surface coated with calcium scale.

Your pool is still too young to make any generalization about SWG use and pH rise. There are too many other confounding factors. Simply maintain proper chemistry levels and give the pool what it needs when it needs it. If you need to use lots of acid this season to keep the pH under control, then do that. It will eventually settle in and, like most pools, it will become easier to maintain.

New pools are like newborns, they keep you up all night and you constantly have to clean up their …

 

[generessler]

For my pool there's a large impact for TA 50-60 vs TA 70-80. pH increase is much slower in the first case. Temperature also makes a big difference. With TA 70+ in mid-summer >80F water, it takes only 2-4 days for 7.4 to increase to 8.0. With TA below 60 it's 8-10 days. SWG vs LQ impact is some fraction of a day. In the fall when water hits the 50's, rise times are double. My plaster is ~16 years old.

 

[mgtfp]

New pools are like newborns, they keep you up all night and you constantly have to clean up their …

Are there nappies (or diapers for those who don't constantly have to stop their pool water from falling into the sky) for pools? And when would be the right time to start potty training?

 

[cwswifty]

There’s a couple of issues that should be considered -

1. You can not compare cold water conditions and warm water conditions easily. Temperature affects a lot of variables and warm water out gases faster than cold water. So your pH rise is going to be seasonal no matter what.

2. Your new plaster could still be emitting some caustic compounds. That will pH rise a continuous issue until the plaster ages.

3. You need to be careful with such low TA fill water and always ensure that your CSI is balanced or only very slightly negative. Cold water is more aggressive towards plaster than warm water and new plaster needs proper calcium saturation or else the water will actually strip the plaster of more caustic calcium compounds thereby causing the pH to rise. TFP has seen this before with newly plastered pools being allowed to sit over winter with aggressive water and then the pool owner opens the pool to find the surface coated with calcium scale.

Your pool is still too young to make any generalization about SWG use and pH rise. There are too many other confounding factors. Simply maintain proper chemistry levels and give the pool what it needs when it needs it. If you need to use lots of acid this season to keep the pH under control, then do that. It will eventually settle in and, like most pools, it will become easier to maintain.

New pools are like newborns, they keep you up all night and you constantly have to clean up their …

Thanks Joyfull. I’m 55 years old with a 4 year old son. Now I have my first pool. What TF have I done?

 

[Homebrewale]

Anecdotally -- a moderator here has a Fiberglass pool in metro Atlanta area. She has a SWCG with low TA fill water. Her pH is steady. Never changes. No acid. With SWCG use.

I had the same experience. I did not add one drop of muriatic acid last year to my pool.

 

[JoyfulNoise]

Thanks Joyfull. I’m 55 years old with a 4 year old son. Now I have my first pool. What TF have I done?

Buy a puppy … trifecta of idiocy (ask me how I know )