Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 7 of 7

Thread: SWG pH rise

  1. Back To Top    #1

    SWG pH rise

    I've read a couple of different things while browsing the forum in hopes of finding a clear answer.
    The first is that a rise in pH comes from increased aeration of the pool water, thus gassing of carbon dioxide.
    The second is that a byproduct of electrolysis (for NaCl water) is Sodium Hydroxide, which is a base.
    I don't know if the NaOH is significant enough to change the pH, but it seems possible.
    Or maybe it is a little of both?

  2. Back To Top    #2
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: SWG pH rise

    The chemical reactions that takes place because of a SWG are net PH neutral (except for chlorine outgassing, which should not be happening). There are quite a few of them, some of which are basic and some of which are acidic, but overall there is no net change in PH. There is an advanced chemistry article in The Deep End that runs through the whole process, go here and search for "pH Rising" and also follow the equations link.

    A SWG creates lots of little hydrogen bubbles, which are usually quite effective at aerating the pool, even when you can't see them. Aeration encourages CO2 outgassing if your TA is at all high (i.e. much above 60ish). That is what causes the PH increase.

    The solution is to lower the TA until the CO2 outgasing rate goes down to close to zero. For most pools that happens when TA is around 60 to 70, though it varies from pool to pool.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. Back To Top    #3
    linen's Avatar
    Join Date
    Jul 2010
    Location
    Twin Cities, MN
    Posts
    8,649

    Re: SWG pH rise

    Just to add to what Jason said, the swg does not really produce NaOH. See:http://www.troublefreepool.com/for-w...174.html#p1139
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

  4. Back To Top    #4

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: SWG pH rise

    There is also the possibility of some chlorine gas not getting fully dissolved and outgassing instead. That would also cause the pH to rise and would not be helped by a lower TA level.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  5. Back To Top    #5

    Re: SWG pH rise

    Ok so the net rise in pH is basically neutral when the chlorine gets used up, however, i would assume that nobody lets all of their chlorine get used up before they add the next dose. So with this constant supply of chlorine coming from the SWG, wouldn't we see a consistently higher pH because of it?

    And I don't fully understand why NaOH is not produced...

  6. Back To Top    #6
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: SWG pH rise

    When you first turn the system on, and FC goes from 0 to say 4, there will be a slight PH increase. From then on, chlorine gets added and chlorine gets used up and as long as the FC level remains essentially constant the two cancel each other out and you won't see subsequent PH changes due directly to the SWG (except for the very usual case of chlorine outgassing, which almost never happens enough to measure).

    Na is not involved in the process inside the SWG. The Na ions remain ions and do not combine with OH ions while in solution. You can see the complete chemical equations about half way down this post, look for the "Salt (SWG) Pool" heading.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  7. Back To Top    #7

    Re: SWG pH rise

    Alright i see what you mean now, thanks for putting it into perspective.
    I's sorry these random questions keep popping into my head and you guys are the ONLY ones who can answer them correctly.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •