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

Thread: ORP and Ozone

  1. Back To Top    #1

    Join Date
    Jul 2009
    Location
    Houston, Texas
    Posts
    21

    ORP and Ozone

    More for geekiness than anything else, is it useful to utilize an ORP meter to determine the ORP in a pool that is primarily, but not exclusively, ozone based (plus a bit of chlorine as a backup). In other words, is ORP an absolute that represents the ORP irrespective of the various oxidizing components in the water, or will the presence of two oxidizers working at the same time effect the reading or require adjustment in order to gauge the "health of the water"? In other other words is an ORP of 730 when the ozone is blasting away and there is .5 ppm of FC equal to 730 with just ozone equal to 730 with just chlorine (assuming the other variables, temp/ph etc...are constant)?
    25,500 gallon gunite pool with Pebbletec and Pebblesheen finishes. 1500 gallon upper pool and spa. 1x2.5 hp Jandy high head two speed pump (main filter). Jandy DEV60 DE filter. Jandy Caretaker in floor cleaning system and 8 port electronic valve. Aqualink RS 12 One Touch controls. 1x2hp Jandy high head pump (leaftrapper). 1x2hp Jandy high head pump (main waterfall/slide). 1x1.5 hp Jandy high head pump (spa falls). Glacier Ice Berg evaporative pool chiller tied into aqualink and leaftrapper pump). Clearwatertech A8e ozone generator (self contained) with 80 gallon contact tank. Jandy LXI heater. Rainbow in-line chlorinator.

  2. Back To Top    #2

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

    Re: ORP and Ozone

    First of all, ORP by itself does not indicate the health of the water. If you add non-chlorine shock (MPS), it will raise the ORP, but won't kill pathogens nearly as quickly as chlorine. ORP measures oxidation-reduction potential, but even then the "potential" to oxidize (i.e. thermodynamics) says nothing about its rate of oxidation nor does it relate to the rate of killing pathogens.

    Second, multiple oxidizers in the water, such as chlorine, ozone and MPS, will all increase ORP so that you will get a mixed reading and not really be able to correlate with the disinfecting power of chlorine alone.

    Third, ORP is not an absolute standard the way that many think. Different sensors not only have different absolute measurements, but also vary in their mV per doubling of hypochlorous acid concentration. I write about this in this post.

    The bottom line is that ORP is useful for process control for automatic chlorine dosing systems where you adjust the ORP setpoint based on actual FC/CYA measurements that you already know are sanitary or are enough to prevent algae growth. The use of other oxidizers such as ozone or MPS will interfere with this process control and could result in the chlorine level getting too low or to zero.

    One other point -- ozone is not a bulk pool water disinfectant. It is supposed to be used in a separate chamber since too much ozone in the pool water will result in too much outgassing and that is a health hazard.
    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"

  3. Back To Top    #3

    Join Date
    Jul 2009
    Location
    Houston, Texas
    Posts
    21

    Re: ORP and Ozone

    Reasonable minds can differ (to a limited extent) on your last point. I use ozone plus a very light residual amount of chlorine. My saturation index is right, ph is right, TA and CH are right, FC is right, the pool looks and feels excellent, no algae. I was just curious about the uses of ORP (and I take your point on process control) measurement. Thought it would be interesting to get the chlorine down to 0 during a period when we weren't using the pool and measure the ORP with just the ozone running. So are you saying that if in that circumstance if I had an ORP of 700 (say), adjusted for temperature and ph, that I wouldn't be assured of a sanitary condition for pool water? Not trying to start an argument but this is a very interesting topic (to me anyway). I know there is ozone circulating past my contact tank into my pool on a constant basis, so I would think that if that is the case then an ORP reading in the range that commercial pools test for and health officials deem to be acceptable I'd be in "good shape"?
    25,500 gallon gunite pool with Pebbletec and Pebblesheen finishes. 1500 gallon upper pool and spa. 1x2.5 hp Jandy high head two speed pump (main filter). Jandy DEV60 DE filter. Jandy Caretaker in floor cleaning system and 8 port electronic valve. Aqualink RS 12 One Touch controls. 1x2hp Jandy high head pump (leaftrapper). 1x2hp Jandy high head pump (main waterfall/slide). 1x1.5 hp Jandy high head pump (spa falls). Glacier Ice Berg evaporative pool chiller tied into aqualink and leaftrapper pump). Clearwatertech A8e ozone generator (self contained) with 80 gallon contact tank. Jandy LXI heater. Rainbow in-line chlorinator.

  4. Back To Top    #4
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: ORP and Ozone

    No, ORP is not a reliable measurement of sanitation. Quite a number of factors influence the ORP reading that have absolutely nothing to do with sanitation (for example dissolved hydrogen gas). In a process control situation you can balance everything just the way you want it and then use ORP automation to maintain a chlorine level (or ozone level, though not chlorine and ozone at the same time). However, that assumes that all else remains the same, which it won't always (which can mean frequent re-calibrations of the ORP target level).
    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

  5. Back To Top    #5

    Join Date
    Jul 2009
    Location
    Houston, Texas
    Posts
    21

    Re: ORP and Ozone

    Again, not being argumentative but just trying to understand. 1) So I could use, in a completely ozone pool, an in-line ORP/PH meter to automatically turn on the ozone when the ORP gets below the target threshold? That assumes that the ozone would ever get me to that threshold but I assume if it didn't the controller would just never turn it off? 2) If other things can effect ORP, than what's to say even in a process control situation that some other factor hasn't effected the ORP reading such that the application of additional sanitizer is not accurate (ie: false high reading such that chlorine is not introduced)?
    25,500 gallon gunite pool with Pebbletec and Pebblesheen finishes. 1500 gallon upper pool and spa. 1x2.5 hp Jandy high head two speed pump (main filter). Jandy DEV60 DE filter. Jandy Caretaker in floor cleaning system and 8 port electronic valve. Aqualink RS 12 One Touch controls. 1x2hp Jandy high head pump (leaftrapper). 1x2hp Jandy high head pump (main waterfall/slide). 1x1.5 hp Jandy high head pump (spa falls). Glacier Ice Berg evaporative pool chiller tied into aqualink and leaftrapper pump). Clearwatertech A8e ozone generator (self contained) with 80 gallon contact tank. Jandy LXI heater. Rainbow in-line chlorinator.

  6. Back To Top    #6

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

    Re: ORP and Ozone

    I agree with Jason as ORP is only useful for process control and not absolute measurement and even for process control it can get interference. In practical ORP situations, one tries to keep such interferences to a minimum, such as not using non-chlorine shock in such a pool. What I describe below would have you at least try and get a baseline ORP level that means something by using a chlorine standard.

    You would first need to "calibrate" your ORP sensor to a standard chlorine level. So let's say you measure it when having an FC that is around 10% of the CYA level or roughly 0.1 ppm FC with no CYA which would kill pathogens reasonably quickly (around 1 minute for a 99% kill of most heterotrophic bacteria) and would prevent algae growth as well. Different sensors would report different ORP according to field data for the Oakton and published charts for the others:

    Oakton: 655 mV
    Chemtrol: 695 mV
    Aquarius: 585 mV
    Sensorex: 430 mV

    Then you could compare your ozone ORP reading in the middle of your pool against that standard. However, ORP measurements for controlling ozone systems are done in the side stream or at the outlet to the pool and not in the bulk pool water so I'm not really sure what you are trying to accomplish here.

    The current EPA limit for ground level ozone is 75 ppb and they are about to lower it more to somewhere between 60 and 70 ppb. For swimming pools and spas, ozone is only allowed as a supplemental oxidation system off-line and a small residual that is usually < 0.1 ppm enters the pool and is intentionally a low amount that does not last. Even Del-Ozone, who is hardly unbiased, says "Ozone's role is actually as the primary sanitizer, but maintaining an ozone residual in the pool that is high enough to ensure continuous in-pool protection from bather-to-bather cross contamination can be expensive; and present the risk of ozone off-gas."

    Del-Ozone goes on to equate ozone levels with ORP where they say that "The ORP reading can range between 750 mV and 900 mV at the point of introduction into the main return line before entering the pool. An ORP of 800 mV is ~0.2 PPM dissolved ozone which equates to ~40 PPM Cl in terms of oxidation and efficacy." For commercial recreation/lap pools, they apply 1.6 ppm over 24 hours to the volume of the pool (that is not a residual, but an equivalent amount injected as water circulates through the ozonator). The time for the CT value of ozone in the side stream where it is injected is 4 minutes in their commercial system. You have to take some of what they say with a grain of salt since they claim that "ozone's reaction with chlorine is minimal" and we know that isn't true as we've seen chlorine demand double in spas when ozone is used and there is no bather load (when there is bather load, chlorine demand is cut in half as ozone can oxidize some of the bather waste).

    Interestingly, their 40 ppm chlorine equivalent to 800 mV doesn't fly with any sensors that I know of. 40 ppm FC (with no CYA) would be closer to 900 mV for both Oakton and Chemtrol and even higher for the other sensors.

    For something like E.coli, ozone has a CT value that is about half that of chlorine, but whereas 0.1 ppm FC with no CYA gives the ORP levels I listed above in the 650-700 mV range for Oakton and Chemtrol, ozone would give an ORP of around 770-780 mV. The Ozone CT value for E.coli is about half that of chlorine so the net result is that the ORP of ozone is higher by around 50 mV than it's true chlorine equivalent in terms of disinfection, but there are so many assumptions here that I wouldn't put a lot of faith in this.

    So roughly speaking if you wanted equivalent killing power with ozone compared to chlorine, you would take your ORP reading with 0.1 ppm FC with no CYA equivalent of chlorine (or an FC that is around 10% of the CYA level) and add 50 mV to that and see if ozone alone with no chlorine reaches that level in the middle of the pool away from the returns. If it did, then you might have equivalent sanitation, but would possibly be at the risk of outgassing too much ozone.

    Rather than go through this mess with ORP, why don't you just measure the ozone level directly using a test kit such as the CHEMetrics K-7402 (there are also test strips that others make, but I'm not sure I'd trust those).

    I really don't understand why you want to try and flood your pool with ozone levels that even the ozonator industry doesn't attempt due both to cost and safety. You might as well just irradiate your entire pool area with UV and ignore the cancerous effects on your skin. That's basically what you are trying to do by exposing yourself to high ozone concentrations, most especially if they outgas.
    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

    Join Date
    Jul 2009
    Location
    Houston, Texas
    Posts
    21

    Re: ORP and Ozone

    Thaks, that is all very helpful and interesting. I'm not actually trying to do anything. I'm just curious after seeing a lot about ORP and chlorine and the different factors that need to be taken into account, and just wondered how it would apply in an ozone situation. As I mentioned, above, while ozone is my primary, I do maintain an appropriate chlorine residual. I was curious about how the various oxidizers would affect the ORP reading in the sense that if I wanted to use an inline ORP meter tied to a controller/pump for liquid chlorine would it be able to adequately measure ORP so as to apply the right amount of chlorine.
    25,500 gallon gunite pool with Pebbletec and Pebblesheen finishes. 1500 gallon upper pool and spa. 1x2.5 hp Jandy high head two speed pump (main filter). Jandy DEV60 DE filter. Jandy Caretaker in floor cleaning system and 8 port electronic valve. Aqualink RS 12 One Touch controls. 1x2hp Jandy high head pump (leaftrapper). 1x2hp Jandy high head pump (main waterfall/slide). 1x1.5 hp Jandy high head pump (spa falls). Glacier Ice Berg evaporative pool chiller tied into aqualink and leaftrapper pump). Clearwatertech A8e ozone generator (self contained) with 80 gallon contact tank. Jandy LXI heater. Rainbow in-line chlorinator.

  8. Back To Top    #8

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

    Re: ORP and Ozone

    So the short answer to that last question is maybe -- if your ORP sensor were located as far away as possible from any returns that would be adding ozone into the water, then perhaps you could get a reasonable proxy reading of the chlorine level. However, if the ozone does persist in the water too much, then it will interfere with any such ORP reading possibly having your chlorine controller shut down to have no chlorine in the water at all.
    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 2009
    Location
    Houston, Texas
    Posts
    21

    Re: ORP and Ozone

    Right, nevermind. I'll just turn the ozone up and sniff the sweet, sweet smell of watermelons. [cough...cough]
    25,500 gallon gunite pool with Pebbletec and Pebblesheen finishes. 1500 gallon upper pool and spa. 1x2.5 hp Jandy high head two speed pump (main filter). Jandy DEV60 DE filter. Jandy Caretaker in floor cleaning system and 8 port electronic valve. Aqualink RS 12 One Touch controls. 1x2hp Jandy high head pump (leaftrapper). 1x2hp Jandy high head pump (main waterfall/slide). 1x1.5 hp Jandy high head pump (spa falls). Glacier Ice Berg evaporative pool chiller tied into aqualink and leaftrapper pump). Clearwatertech A8e ozone generator (self contained) with 80 gallon contact tank. Jandy LXI heater. Rainbow in-line chlorinator.

  10. Back To Top    #10

    In the Industry

    Join Date
    Jul 2009
    Location
    London and France
    Posts
    574

    Re: ORP and Ozone

    Just had a chat on the phone with the Seimens tech's and they recommend the new Cl2 sensors rather than ORP as the fluctuations in ORP are too great with low chlorine figures and of course the CYA effect on ORP

  11. Back To Top    #11

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

    Re: ORP and Ozone

    So Chemtrol and some others had chlorine sensors years ago, but they weren't considered very reliable. I would assume things have improved since then. The chlorine sensors actually measure hypochlorous acid since they use a selective membrane so even with CYA in the water you get a true chlorine reading, BUT that means one should target something like 0.1 ppm FC equivalent with no CYA (or around 0.05 ppm HOCl), otherwise one will have excessively high chlorine levels.
    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"

  12. Back To Top    #12

    In the Industry

    Join Date
    Jul 2009
    Location
    London and France
    Posts
    574

    Re: ORP and Ozone

    Yes it would seem so, Chemtrol and Prominent are leading in this area I belive.

Posting Permissions

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