Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 15 of 15

Thread: Is chlorine more effective with a lower pH?

  1. Back To Top    #1

    Join Date
    Mar 2011
    Location
    Orlando, FL
    Posts
    12

    Is chlorine more effective with a lower pH?

    I have been trying to understand the more advanced concepts of what is happening to the chlorine in the water. I came across this article about "Water Treatment To Prevent Emitter Plugging"

    http://fawn.ifas.ufl.edu/tools/irrigati ... ance/four/

    It looks like it would be helpful to lower the pH to near the load end of the acceptable range in order to get the most effect from the chlorine when fighting algae, especially cleaning up a swamp.

    Your comments please.

    Gary
    Viking Pools Freeport 12' x 25' Fiberglass 6000 Gallon Screened - Hayward Pro-Grid Vertical D.E. Filter DE2420 Hayward Superpump 1HP - Zodiac Pacer Cleaner - Pool Pilot Digital - TF-100 test kit - Central Florida Thanks to TFP Pool School, SWCG and the Pool Calculator, taking care of the pool is easy!

  2. Back To Top    #2
    frogabog's Avatar
    Join Date
    Jul 2010
    Location
    Portland, Oregon
    Posts
    1,578

    Re: Is chlorine more effective with a lower pH?

    Could be why the pool school shocking information here says to lower ph to 7.0-7.2 (IIRC) while shocking. ???

    Now, I'd like to know if standard min/target is less effective at higher ph levels (say, 7.7).
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

  3. Back To Top    #3
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: Is chlorine more effective with a lower pH?

    This is really only true when there isn't any CYA in the water. As soon as there is any CYA in the water, almost all of the chlorine effectiveness variation with PH goes away. For details, see this post.

    frogabog, Pool School doesn't say to lower PH to 7.0 to 7.2 when shocking that I'm aware of. And if it does it is wrong.

    All of our recommendations have already taken this kind of thing into account.
    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

  4. Back To Top    #4

    Join Date
    Mar 2011
    Location
    Orlando, FL
    Posts
    12

    Re: Is chlorine more effective with a lower pH?

    Jason, That post helped a lot.

    The pool calculator is the BEST!

    Gary
    Viking Pools Freeport 12' x 25' Fiberglass 6000 Gallon Screened - Hayward Pro-Grid Vertical D.E. Filter DE2420 Hayward Superpump 1HP - Zodiac Pacer Cleaner - Pool Pilot Digital - TF-100 test kit - Central Florida Thanks to TFP Pool School, SWCG and the Pool Calculator, taking care of the pool is easy!

  5. Back To Top    #5
    TripleB4me's Avatar
    Join Date
    Jun 2007
    Location
    Maryland
    Posts
    224

    Re: Is chlorine more effective with a lower pH?

    turning-your-green-swamp-back-into-a-sparking-oasis-t4147.html says: adjust the PH to between 7.2 and 7.4 before you start. Chlorine is more effective at lower PH levels. Also, the PH test is not reliable at high FC levels. The FC level is going to be high for several days, so you need to get the PH right before you start.
    20x40 IG Vinyl, 1.5 HP Whisperflo, Sta-Rite System 3 (300) Sq. ft Cart
    Intellichlor IC40 SWCG, 125,000 BTU Pentair heatpump, Polaris 280
    7' IG FG Spa, 2 HP Whisperflo, Pentair Dynamic III Cart (100) Sq. ft

  6. Back To Top    #6
    frogabog's Avatar
    Join Date
    Jul 2010
    Location
    Portland, Oregon
    Posts
    1,578

    Re: Is chlorine more effective with a lower pH?

    Sorry, I got the numbers wrong, 7.2-7.4 (not 7.0-7.2). I should have checked before I posted. I am however referring to the url that TrippleB4me referenced above.
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

  7. Back To Top    #7
    TripleB4me's Avatar
    Join Date
    Jun 2007
    Location
    Maryland
    Posts
    224

    Re: Is chlorine more effective with a lower pH?

    Quote Originally Posted by frogabog
    Sorry, I got the numbers wrong, 7.2-7.4 (not 7.0-7.2). I should have checked before I posted. I am however referring to the url that TrippleB4me referenced above.
    frogabog, when I saw your post I too remembered reading that chlorine was more effective at lower pH levels, I wasn't picking at your numbers but agreeing that it has been said that chlorine is reported to work better at lower pH levels, which to me, contradicted Jason's response.
    20x40 IG Vinyl, 1.5 HP Whisperflo, Sta-Rite System 3 (300) Sq. ft Cart
    Intellichlor IC40 SWCG, 125,000 BTU Pentair heatpump, Polaris 280
    7' IG FG Spa, 2 HP Whisperflo, Pentair Dynamic III Cart (100) Sq. ft

  8. Back To Top    #8
    frogabog's Avatar
    Join Date
    Jul 2010
    Location
    Portland, Oregon
    Posts
    1,578

    Re: Is chlorine more effective with a lower pH?

    LOL, yeah but Jason's the "King of the Jungle"...

    I bow to him and do what the Lion King says to do, else I just end up having to flog myself and live apart from the pack :~}
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

  9. Back To Top    #9
    TripleB4me's Avatar
    Join Date
    Jun 2007
    Location
    Maryland
    Posts
    224

    Re: Is chlorine more effective with a lower pH?

    I agree...bow to the King
    20x40 IG Vinyl, 1.5 HP Whisperflo, Sta-Rite System 3 (300) Sq. ft Cart
    Intellichlor IC40 SWCG, 125,000 BTU Pentair heatpump, Polaris 280
    7' IG FG Spa, 2 HP Whisperflo, Pentair Dynamic III Cart (100) Sq. ft

  10. Back To Top    #10
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: Is chlorine more effective with a lower pH?



    You found an old reference, which I have now fixed. I was half right, it didn't say 7.0 to 7.2
    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

  11. Back To Top    #11

    Join Date
    Jul 2010
    Location
    England, UK
    Posts
    156

    Re: Is chlorine more effective with a lower pH?

    I was playing with some numbers. If the pH rises from 7.5 to 7.8, then the HOCl concentration falls from (say) 10% to 9% of the overall free chlorine level (or thereabouts). It sounds like hardly any change. But to look at it another way, your chlorine is only 90% as effective at pH 7.8 as it was at pH 7.5.

    When you're working with such tiny quantities to start with, perhaps it does matter. I find that pH does make a difference in how well my pool runs.

    However, perhaps the pH has an influence on other things, like reaction rates of making combined chlorine.
    90k litres, outdoor in ground pool, concrete, painted (I hate paint)
    Sta-Rite 5P2R 1.5 Hp pump, undersized sand filter (needs upgrading).

  12. Back To Top    #12

    Join Date
    Dec 2009
    Location
    Europe
    Posts
    89

    Re: Is chlorine more effective with a lower pH?

    All the pools I maintain (13 of them) have a PH of 7.6 to 7.8 and most are public pools and I don't have any problems with my HOCl levels. I also have the lower end ALK so a high PH really helps my balance. When considering what levels you are going to have never take them in isolation but consider what effect it will have overall when all other parameters are put into the boiling pot so to speak.

  13. Back To Top    #13

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

    Re: Is chlorine more effective with a lower pH?

    Quote Originally Posted by loop_pea
    I was playing with some numbers. If the pH rises from 7.5 to 7.8, then the HOCl concentration falls from (say) 10% to 9% of the overall free chlorine level (or thereabouts).
    I don't know what you are using to play around with the numbers, but if you use my spreadsheet, then with an FC that is 3 and a CYA that is 30 ppm, at a pH of 7.5 the HOCl is 0.042 ppm or 1.40% of the FC level while at a pH of 7.8 it is 0.038 ppm or 1.27% of the FC level. Nevertheless, your point of the chlorine level at a pH of 7.8 being 90% of what it was at a pH of 7.5 is still true. This should not normally make any noticeable difference.

    As for disinfection by-products, there is more nitrogen trichloride produced at lower pH while there are more trihalomethanes (such as chloroform) produced at higher pH.

    Quote Originally Posted by loop_pea
    I find that pH does make a difference in how well my pool runs.
    Can you be more specific? What kinds of differences do you notice? As Freelancer noted, a higher pH can be more stable with regard to carbon dioxide outgassing. This effect, as well as TA, are shown in this chart. Roughly speaking, the amount of carbon dioxide in the pool is about half as much at 7.8 as at 7.5.
    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"

  14. Back To Top    #14

    Join Date
    Jul 2010
    Location
    England, UK
    Posts
    156

    Re: Is chlorine more effective with a lower pH?

    chemgeek, i was using your spreadsheet

    Apologies for my maths. It's up the spout at the moment, even with a calculator, but the 90% is the point I was trying to convey.

    It feels like when you're working with HOCl levels of only a few percent, then the magnitude of the change is relatively large compared to where you started, and it might push you over a threshold where there isn't enough HOCl to deal with bather waste in the pool fast enough.

    In the UK the advice is to keep CC at less than half FC because it influences the chemical reactions. we're told that if CC is too high relative to FC then it encourages the production of nitrogen trichloride.

    Low pH never comes into it for us, as we start with a fresh fill of high TA water. After a bit of a battle on startup, the TA and pH have stabilised nicely at around 130 and 7.6 respectively (trichlor pool).

    However, in my experience high pH also coincides with more nitrogen trichloride production, which is the opposite of what's generally said.

    I've been trying to get my head around the complex relationship between all these things, FC, CC and pH and their influence on pool smell. I really hate pool smell.
    90k litres, outdoor in ground pool, concrete, painted (I hate paint)
    Sta-Rite 5P2R 1.5 Hp pump, undersized sand filter (needs upgrading).

  15. Back To Top    #15

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

    Re: Is chlorine more effective with a lower pH?

    I think you are mixing up your interpretation of what the FC and HOCl levels mean. Just because the HOCl level is very low does not necessarily mean that there isn't enough HOCl to deal with bather waste fast enough, at least in outdoor residential pools. There is plenty of capacity to handle the bather waste in the FC level as the FC converts to HOCl quickly (half of the FC can convert to HOCl in 1/4th of a second, if needed). The very low HOCl level is nevertheless enough to kill most pathogens quickly (see this link for some kill times) and is enough to prevent algae growth. It oxidizes some bather waste reasonably quickly where ammonia is mostly oxidized in a matter of a few hours, though in practice this is continual (i.e. ammonia isn't all dumped in at once). Urea is slow to oxidize by chlorine, but this and other organics most likely get handled when chlorine breaks down by the UV in sunlight forming hydroxyl (and chlorine) free radicals that are very powerful oxidizers. For this analysis I assume the FC is at least 7.5% of the CYA level (see the Chlorine / CYA Chart. It is true that if your FC/CYA ratio is too low, then oxidation rates may get too low as well.

    The CC should not be half of the FC but should rather be fairly low, usually <= 0.5 ppm and most often in outdoor residential pools it is <= 0.2 ppm. You say you use Trichlor pucks/tabs, but for every 10 ppm FC added by Trichlor, it increases CYA by 6 ppm. So even with 2 ppm FC per day chlorine usage, Trichlor will increase CYA by over 35 ppm PER MONTH. The higher CYA level is likely what causes you problems unless you proportionately raise the FC level as the CYA level climbs.

    High pH has less nitrogen trichloride, but more trichloromethanes such as chloroform. I suspect your high CYA level is causing a buildup of monochloramine and other combined chlorine. Do you know your CYA level? Are you talking about an indoor pool or an outdoor pool exposed to sunlight? Residential low bather-load pool or commercial/public high bather-load pool?

    A properly managed outdoor residential pool won't have any bad smell. It will only have the faintest of bleach-like chlorine smell if you churn up the water a bit. You might smell some chloramines (mostly monochloramine) on your skin if you get out of the water since your sweat will continue to react with chlorine, but that's about it. So something is not right with your pool if you are having trouble with its smell. That was the problem you were having in this thread about a year ago when you first came to this forum.
    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"

Posting Permissions

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