Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 13 of 13

Thread: Accurate pH test during shock levels with R-007?

  1. Back To Top    #1
    JesseWV's Avatar
    Join Date
    Apr 2011
    Location
    North Central WV
    Posts
    526

    Accurate pH test during shock levels with R-007?

    Can R-007 be used to neutralize high FC before performing the pH test to get an accurate reading or will this further interfere with the chemistry?
    16k gal, 28'x3.5', Vinyl A/G, 1hp Pentair Dynamo 2-speed Pump, Hayward S160T Sand Filter, Intermatic HB800RCL Digital Timer, Intex 8110 SWG, TF-100 Test Kit, SpeedStir Author: Jesse's Graphical Pool Testing Log

  2. Back To Top    #2
    Richard320's Avatar
    Join Date
    Jan 2010
    Location
    San Dimas, CA (LA County)
    Posts
    18,768

    Re: Accurate pH test during shock levels with R-007?

    I'm pretty sure it messes things up.

    How about you be our guinea pig? Test your tap water pH, then add some R-007 and try it again.

    I expect a full report by morning.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  3. Back To Top    #3
    JesseWV's Avatar
    Join Date
    Apr 2011
    Location
    North Central WV
    Posts
    526

    Re: Accurate pH test during shock levels with R-007?

    WP_20130529_006.jpg
    Normal chlorine level, accurate pH reading.

    WP_20130529_005.jpg
    Shock level chlorine, pH reading is inaccurately high.

    WP_20130529_007.jpg
    Chlorine neutralized, pH still reading high.


    Obviously there is still something that the R-007 is not neutralizing which is still affecting the pH test.

    At least now I know, and knowing is half the battle! :knowing:
    16k gal, 28'x3.5', Vinyl A/G, 1hp Pentair Dynamo 2-speed Pump, Hayward S160T Sand Filter, Intermatic HB800RCL Digital Timer, Intex 8110 SWG, TF-100 Test Kit, SpeedStir Author: Jesse's Graphical Pool Testing Log

  4. Back To Top    #4
    Richard320's Avatar
    Join Date
    Jan 2010
    Location
    San Dimas, CA (LA County)
    Posts
    18,768

    Re: Accurate pH test during shock levels with R-007?

    Excellent! Bookmarked for future reference.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  5. Back To Top    #5
    UnderWaterVanya's Avatar
    Join Date
    Jun 2012
    Location
    Mint Hill, NC
    Posts
    2,589

    Re: Accurate pH test during shock levels with R-007?

    My understanding is that the phenol red from Taylor is already buffered and that neutralizers have an impact themselves on pH.

    Sent via Tapatalk...
    Inlaws Pool Boy since June 14th 2012, Pool built ~ 2003, In-Ground, 16'x32'
    13500 gal, Vinyl Liner, Fiberglass Slide, TF-100 Test Kit, Hayward 210T
    sand filter, A.O. Smith 1.5HP main pump motor (C48L2N134C1),
    Hayward SuperPump (model ?), Polaris 380 & PB4 Booster Pump

  6. Back To Top    #6

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

    Re: Accurate pH test during shock levels with R-007?

    Taylor uses a proprietary blend of chlorine neutralizers that try to net out to not change the pH when chlorine is present. The sodium thiosulfate in the R-0007, however, tends to be of high pH and will not react with chlorine in a pH neutral way so will affect the pH test which is why Taylor recommends not to use it. With CYA in the water, the pH test may still be OK for a short time even at FC higher than 10 ppm, but for simplicity and to be conservative we generally say not to consider the pH test to be valid when the FC is higher than 10 ppm.
    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"

  7. Back To Top    #7
    JesseWV's Avatar
    Join Date
    Apr 2011
    Location
    North Central WV
    Posts
    526

    Re: Accurate pH test during shock levels with R-007?

    So what amount of sodium thiosulfate should to be added to what volume of water to neutralize a reasonable amount of chlorine without being considered "heavily used" and thus also causing an erroneous high pH reading?

    Also, I have to wonder what the break point is for getting a correct reading even at high FC levels? This makes me want to do some experimenting.

    Quote Originally Posted by chem geek
    No, I would leave the pH alone. You don't need it higher to kill algae. And odds are that his pH reading may be correct. When the pH reads falsely high, it's false reading is quite high. It won't falsely read a lower reading. If you get a reading of 7.5 or below, odds are it's a correct reading. It's when it looks like 7.8 or 8.0 or higher that it may not be that high. Remember what Taylor says about this process:

    FALSE READINGS: high levels of chlorine (usually > 10 ppm) will quickly and completely convert phenol red into another pH indicator (chlorphenol red). This new indicator is a dark purple when the water's pH is above 6.6. Unfortunately, some pool operators mistake the purple color for dark red and think the pool water is very alkaline and wrongly add acid to the pool.

    When a sanitizer level is not extreme, only some of the phenol red may convert to chlorphenol red. However, purple + orange (for example, pH 7.4) = red. This error is more subtle as no purple color is observed and the operator does not suspect that a false high pH reading has been produced. Some operators neutralize the sanitizer first by adding a drop of chlorine neutralizer (i.e. sodium thiosulfate). However, thiosulfate solutions have a high pH and, if heavily used, may cause a false higher sample pH.
    The part that Taylor is missing is that the "quickly and completely" occurs when there is no CYA in the water. With CYA in the water it appears that this conversion process takes longer, perhaps 30 seconds or a minute, depending on the FC/CYA ratio. We have just been conservative and simplistic about high chlorine interfering with pH just in case the CYA is low or people don't take a reading quickly. Also, adding a hypochlorite source of chlorine in large quantities WILL raise the pH significantly, especially when CYA is present and borates are not used and if the TA isn't high.
    16k gal, 28'x3.5', Vinyl A/G, 1hp Pentair Dynamo 2-speed Pump, Hayward S160T Sand Filter, Intermatic HB800RCL Digital Timer, Intex 8110 SWG, TF-100 Test Kit, SpeedStir Author: Jesse's Graphical Pool Testing Log

  8. Back To Top    #8
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: Accurate pH test during shock levels with R-007?

    You can't win with sodium thiosulfate and the PH test. Adding enough to have any meaningful effect on the FC level will throw off the PH reading. If you absolutely must have PH readings when FC levels are high, you will need a completely different approach. However, there really is hardly any situation that comes up when you are following our recommendations where you need to measure PH at high FC levels.

    The PH test gets less and less precise as the FC level goes from 10 to about 18. Somewhere between an FC of 18 and 21 the results switch to being completely unusable as the indicator dye gets chemically converted to a different compound by the chlorine.
    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

  9. Back To Top    #9
    JesseWV's Avatar
    Join Date
    Apr 2011
    Location
    North Central WV
    Posts
    526

    Re: Accurate pH test during shock levels with R-007?

    So ideally pH levels should be adjusted before shocking. Obviously if you've already added shock level chlorine it's too late. Should pH really be ignored until after the shock process is over?

    This bothers me because one of the criteria for completing the shock process is "the water is clear." I can see this being a problem for someone with a high CSI. With improper pH the water may never become clear due to calcium precipitates. I suppose the filter will eventually get it but that could take much longer than necessary if the pH was in the proper range in the first place, correct?

    Quote Originally Posted by JasonLion
    You can't win with sodium thiosulfate and the PH test. Adding enough to have any meaningful effect on the FC level will throw off the PH reading. If you absolutely must have PH readings when FC levels are high, you will need a completely different approach. However, there really is hardly any situation that comes up when you are following our recommendations where you need to measure PH at high FC levels.

    The PH test gets less and less precise as the FC level goes from 10 to about 18. Somewhere between an FC of 18 and 21 the results switch to being completely unusable as the indicator dye gets chemically converted to a different compound by the chlorine.
    16k gal, 28'x3.5', Vinyl A/G, 1hp Pentair Dynamo 2-speed Pump, Hayward S160T Sand Filter, Intermatic HB800RCL Digital Timer, Intex 8110 SWG, TF-100 Test Kit, SpeedStir Author: Jesse's Graphical Pool Testing Log

  10. Back To Top    #10
    Richard320's Avatar
    Join Date
    Jan 2010
    Location
    San Dimas, CA (LA County)
    Posts
    18,768

    Re: Accurate pH test during shock levels with R-007?

    Quote Originally Posted by JesseWV
    So ideally pH levels should be adjusted before shocking. Obviously if you've already added shock level chlorine it's too late. Should pH really be ignored until after the shock process is over?

    This bothers me because one of the criteria for completing the shock process is "the water is clear." I can see this being a problem for someone with a high CSI. With improper pH the water may never become clear due to calcium precipitates. I suppose the filter will eventually get it but that could take much longer than necessary if the pH was in the proper range in the first place, correct?

    Quote Originally Posted by JasonLion
    You can't win with sodium thiosulfate and the PH test. Adding enough to have any meaningful effect on the FC level will throw off the PH reading. If you absolutely must have PH readings when FC levels are high, you will need a completely different approach. However, there really is hardly any situation that comes up when you are following our recommendations where you need to measure PH at high FC levels.

    The PH test gets less and less precise as the FC level goes from 10 to about 18. Somewhere between an FC of 18 and 21 the results switch to being completely unusable as the indicator dye gets chemically converted to a different compound by the chlorine.
    If the pH is correct, or slightly at the low end, there should be no problem. While bleach is alkaline, after it breaks down the net pH change is very small.

    Now you also see why we get so insistent upon a full set of readings. If someone intends to start the season with astronomical CH and/or CYA and a green pool, we encourage a partial drain before pouring expensive chemicals in.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  11. Back To Top    #11

    In the Industry

    Join Date
    May 2013
    Location
    Deep East Texas
    Posts
    76

    Re: Accurate pH test during shock levels with R-007?

    In the CPO class they taught that the higher pH level the less effective the chlorine will be at activating and killing organics. Was this just bunk or is there validity in those lessons. If so I would think that it requires pH in the lower side before undertaking the shock process.
    In ground 25,000 gallon - vinyl liner - Sand filter - residential pool
    Also maintain two commercial 190,000 gallon competitive indoor bromine facilities -9x Sand filters

  12. Back To Top    #12
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: Accurate pH test during shock levels with R-007?

    Chlorine is significantly less effective when the PH is high and CYA is zero. As soon as you add CYA that effect is almost completely eliminated. We deal with nearly all outdoor pools, which invariably are using CYA, so the PH effect on chlorine can normally be ignored as the CYA cancels it out.
    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

  13. Back To Top    #13

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

    Re: Accurate pH test during shock levels with R-007?

    There's a double-edged sword effect when CYA is present. CYA buffers hypochlorous acid so resists changes to its concentration when the pH changes, but the other way around is also true which is that when a hypochlorite source of chlorine is added, the pH rises more than it otherwise would if there were no CYA. This thread discusses whether one should lower the pH before shocking.

    If there is no CYA in the water, but one has a TA of 80 ppm, then if one adds 10 ppm FC using chlorinating liquid or bleach then the pH would rise from 7.5 to 7.76 so not a huge amount. Though the active chlorine (hypochlorous acid) level would drop by about 50% going from 7.5 to 8.0, it's absolute level is already very, very high at 3.4 ppm. When CYA is present, the active chlorine level drops by around 15% for that same pH change so not very much.

    Now let's shock the pool with an FC that is 40% of the CYA level, assuming we are starting with no FC and that the TA is 80 ppm:

    12 ppm FC added with 30 ppm CYA: pH goes from 7.5 to 8.26; active chlorine is 0.22 ppm (at pH 7.5 it would be 0.29 ppm)
    32 ppm FC added with 80 ppm CYA: pH goes from 7.5 to 8.95; active chlorine is 0.18 ppm (at pH 7.5 it would be 0.31 ppm)

    So the rise in pH does lower the active chlorine level by about 1/3rd from its intended target though shocking just accelerates things and there's not a single "magic" number for it. The bigger concern is how high the pH rises, especially if there are metals in the water since that can lead to metal staining. It could also cause calcium carbonate precipitation (scaling) though in practice may just make the water more dull/cloudy which wouldn't be noticeable with algae turning from green to gray though it may lead to a slower clearing of cloudy water since some of that cloudiness is associated with calcium carbonate and not dead algae.
    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
  •