Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 12 of 12

Thread: Sources of acid demand

  1. Back To Top    #1

    Join Date
    Oct 2007
    Location
    Valrico, FL
    Posts
    502

    Sources of acid demand

    I would like some help in identifying some possible sources of acid demand in my pool. I have a salt pool with a SWCG. First my most recent numbers:
    FC 3.0
    TC 3.2
    CC 0.2
    pH 7.6
    TA 80
    CH 370
    CYA 80
    Borates 30
    Salt 3100
    Temp 90F

    I have installed an acid feed pump that maintains the pH more or less constant. Anyway I am adding about 32 oz of 31% acid per week. Some sources of acid demand that I know of:

    1. CO2 out gassing. This is a possibility. However my TA has not changed 10 ppm in over a month. It is my understanding that CO2 out gassing at a constant pH will tend to decrease the TA. Using my Colorq it appears that the TA has changed by less than 5 ppm in a month.

    2. Plaster curing. Another possibility. However the pool was filled at the end of October. It is now August so the plaster is about 10 months out. I would expect that the acid demand from curing plaster to be rather small.

    3. Rain. I live in west central Florida. In the summer we have very high rainfalls. I am pumping out 1 to 2 inches of water from the pool each week. I don't know what effect this would have on the acid demand, but is causing me to add salt and CYA

    I am open to any more ideas.

    Thank You,
    Donald
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

  2. Back To Top    #2
    mas985's Avatar
    Join Date
    May 2007
    Location
    Pleasanton, CA
    Posts
    9,928

    Re: Sources of acid demand

    Quote Originally Posted by dschlic1
    I would like some help in identifying some possible sources of acid demand in my pool. I have a salt pool with a SWCG. First my most recent numbers:
    FC 3.0
    TC 3.2
    CC 0.2
    pH 7.6
    TA 80
    CH 370
    CYA 80
    Borates 30
    Salt 3100
    Temp 90F

    I have installed an acid feed pump that maintains the pH more or less constant. Anyway I am adding about 32 oz of 31% acid per week. Some sources of acid demand that I know of:

    1. CO2 out gassing. This is a possibility. However my TA has not changed 10 ppm in over a month. It is my understanding that CO2 out gassing at a constant pH will tend to decrease the TA. Using my Colorq it appears that the TA has changed by less than 5 ppm in a month.

    This is probably the cause. Even though TA has not changed does not mean that the PH will not rise. Acid will lower the TA as well as PH so if there is anything adding TA to the pool, and there are a lot of sources, then the PH will continue to rise and TA could remain the same. This happens in my pool. If you did not have some other source of TA from somewhere, over time the addition of acid will continue to lower TA.

    2. Plaster curing. Another possibility. However the pool was filled at the end of October. It is now August so the plaster is about 10 months out. I would expect that the acid demand from curing plaster to be rather small.

    Even though the plaster may completely cure, there is a small film of solid plaster dust which can take a while to complete dissolve. Mine took well over a year before it was completely gone and I had to add quite a bit of acid.

    3. Rain. I live in west central Florida. In the summer we have very high rainfalls. I am pumping out 1 to 2 inches of water from the pool each week. I don't know what effect this would have on the acid demand, but is causing me to add salt and CYA

    I'm not sure but I would think that a basic rain is somewhat unusual. Rain is usually acidic.

    I am open to any more ideas.

    Thank You,
    Donald
    More to add:

    4) Fill water - This may not impact you as much given the amount of rain you are seeing. I have very high TA fill water which tends to keep the TA high and raises the PH.

    My guess is that the plaster is still adding TA to the water and adding acid only keeps it steady. The SWG will cause the PH to rise unless the TA is kept really low.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

  3. Back To Top    #3
    Guest

    Re: Sources of acid demand

    Rain aerates the water and will cause CO2 to outgas, btw.

  4. Back To Top    #4
    mas985's Avatar
    Join Date
    May 2007
    Location
    Pleasanton, CA
    Posts
    9,928

    Re: Sources of acid demand

    Quote Originally Posted by waterbear
    Rain aerates the water and will cause CO2 to outgas, btw.
    Good point, completely forgot about that.
    Mark
    Hydraulics 101; Pump Ed 101; Pump and Pool Spreadsheets; Pump Run Time Study; DIY Acid Dosing; DIY Cover Roller
    18'x36' 20k plaster, 1/2 HP 2sp pump, Aqualogic PS8 SWCG, 420 sq-ft Cartridge, Solar, 6 jet spa, 1 HP jet pump, 400k BTU NG Heater

  5. Back To Top    #5

    Join Date
    Oct 2007
    Location
    Valrico, FL
    Posts
    502

    Re: Sources of acid demand

    I forgot to add my SWCG settings. I have an AquaPlus unit with the T-15 cell. The current SWCG setting is 10%. During the week I run the filter from 10 am to 7 pm, and on weekends from 8 am to 7 pm. The AquaPlus has a two hour cycle time. So on weekdays I have five cycles of 12 minutes each (one hour total run time) and on Saturday and Sunday I have six cycles of 12 minutes for a runtime of 72 minutes each day. The T-15 cell is rated to produce 1.45 lbs of chlorine per day, so for a weekday the daily production is 0.06 lbs of chlorine, and on weekends is 0.073 lbs. Total weekly production is 0.45 lbs of chlorine.
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

  6. Back To Top    #6
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,887

    Re: Sources of acid demand

    A conversation about the chemistry of SWGs has been split off to this topic. JasonLion
    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

    Join Date
    Oct 2007
    Location
    Valrico, FL
    Posts
    502

    Re: Sources of acid demand

    Acid will lower the TA as well as PH so if there is anything adding TA to the pool, and there are a lot of sources, then the PH will continue to rise and TA could remain the same. This happens in my pool. If you did not have some other source of TA from somewhere, over time the addition of acid will continue to lower TA.
    What other processes other than plater curing can raise pH and TA?
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

  8. Back To Top    #8

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,085

    Re: Sources of acid demand

    The pH can rise from outgassing of carbon dioxide with no change in TA. The TA can rise from evaporation and refill of water since fill water has some TA in it and usually the fill water doesn't affect the pH very much. So a combination of the two can lead to both pH and TA rising over time.

    As you mentioned, the curing of plaster can increase both pH and TA. Corrosion of pool plaster (from a low saturation index) can likewise lead to a rise in pH and TA.

    Other than the above, the only other thing I can think of is chemicals (e.g. pH Up or Alkalinity Up or Borax or Lye) or stuff that gets into the pool of sufficient quantity that is alkaline.
    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"

  9. Back To Top    #9

    Join Date
    Jul 2007
    Location
    Rockville, CA
    Posts
    99

    Re: Sources of acid demand

    Since rain can cause sufficient aeration to increase pH levels, I would assume the aeration provided by a spillover spa or sheer descents would have a similar effect. I have lots of wind where I live, and would assume this would have a similar effect, as well.
    20K inground gunite w/ Aqua Logic automation and chlorination Sta-Rite 400 K natural gas heater and cartridge filter 2 HP pump 1.5 HP spa bubbler for spillover spa 1 HP dedicated Letro Legend cleaner
    H2O: two parts Heart and one part Obsession. ~Author Unknown

  10. Back To Top    #10

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,085

    Re: Sources of acid demand

    You are correct. Increasing the rate of outgassing of carbon dioxide will increase the rate of pH rise. So a higher TA, lower pH, or more air-water mixing such as aeration from rain, wind, spillover, fountain, waterfall, shower, splashing, returns turned up, will all increase the rate of pH rise.
    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"

  11. Back To Top    #11

    Join Date
    Oct 2007
    Location
    Valrico, FL
    Posts
    502

    Re: Sources of acid demand

    Well it sounds like I am up the creek on reducing my acid demand. I have not filled the pool from tap water for over two to three months. The only fill is from rain. I also have not added anything to the pool expcept salt and CYA.
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

  12. Back To Top    #12
    Guest

    Re: Sources of acid demand

    Quote Originally Posted by dschlic1
    Well it sounds like I am up the creek on reducing my acid demand. I have not filled the pool from tap water for over two to three months. The only fill is from rain. I also have not added anything to the pool expcept salt and CYA.
    Try dropping your TA to 60 ppm and increasing the borates to 50 ppm.

Posting Permissions

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