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Thread: We don't recommend ORP

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    We don't recommend ORP

    Quote Originally Posted by JasonLion View Post
    By the by, we don't recommend any brand of ORP based control for outdoor residential pool.
    Hi Jason, I've seen you say that a few times already, but I have not been able to find a good thread on why. I would like to read why you make that recommendation. Can you point me in the right direction?
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    Patrick_B's Avatar
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    Re: We don't recommend ORP

    I've said the same thing many times, but since you are asking him, I'll let Jason answer.
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    JasonLion's Avatar
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    Re: We don't recommend ORP

    ORP does not reliably correspond to FC level. Contrary to a paper put out by a person working for a company that sells ORP systems, FC level is the best indicator of sanitation, not ORP. There are many different things that can affect the ORP reading, only some of which correspond to the FC level. In a commercial pool you can get a professional operator to re-calibrate the relationship daily, so it can be worthwhile in that context, but for home use that is the exact opposite of what you want.

    There are far more reliable and less expensive system that are readily available and work just as well. ORP requires frequent maintaince and expensive probe replacement, when simple percentage or timer based systems work just as well in residential pools.

    ORP systems have known issues with SWG based systems that cause the combination of ORP and SWG to to completely and utterly not work a significant percentage of the time. SWGs add dissolved hydrogen gas to the water when they are active. Dissolved hydrogen gas pushes the ORP level down fairly rapidly, so you often get the exact opposite reaction from what is intended. In pools with low hydrogen outgassing rates, this results in the ORP system calling for constant chlorine addition for hours or days at a time with no correspondence to the FC level.

    ORP systems require fairly low CYA levels, which result in significantly increased chlorine consumption, and thus higher costs.

    ORP systems require very tight PH regulation. This requires additional equipment and management which would not otherwise be required.
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    Re: We don't recommend ORP

    I found an article that describes what exactly ORP is and how it is measured, which gave me more context for the reasoning behind your statements.

    Thank you!
    39' x 18' IG 3.5X4.5X9 34k gallon w/ raised spa, 3 stone scupers
    Jandy 60 SqFt DE, Jandy PDA PS6, Jandy JXi400 heater, Jandy 2.0 EPump w/SVRS
    A&A Manufacturing ICS w/G4 venturi heads
    2 incandescent lights in pool, 1 in spa.

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    Mod Squad jblizzle's Avatar
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    Re: We don't recommend ORP

    Why not post the article to add as reference?
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    Re: We don't recommend ORP

    Quote Originally Posted by jblizzle View Post
    Why not post the article to add as reference?
    Can do!

    http://www.rhtubs.com/ORP.htm
    39' x 18' IG 3.5X4.5X9 34k gallon w/ raised spa, 3 stone scupers
    Jandy 60 SqFt DE, Jandy PDA PS6, Jandy JXi400 heater, Jandy 2.0 EPump w/SVRS
    A&A Manufacturing ICS w/G4 venturi heads
    2 incandescent lights in pool, 1 in spa.

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    Patrick_B's Avatar
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    Re: We don't recommend ORP

    I fight ORP Probes on a near daily basis. Almost daily, I must tell them what they see, and not what they think is there.
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    JasonLion's Avatar
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    Re: We don't recommend ORP

    That is a fairly reasonable article. However, they do make a few mistakes.

    ORP is not the only way of measuring sanitizer levels. There are direct reading chlorine probes available. They are noticeably more expensive and they to get fouled after not too long, but they do measure the FC level directly, without the problems of ORP.

    The variation in chlorine effectiveness with PH changes they talk about is only true when no CYA is being used. Once CYA is in the water the variation with PH almost goes away. There is still a small effect as PH changes, but it is small enough to ignore. However, an ORP sensor does not track this change in behavior, and remains very sensitive to PH changes.

    Finally, their comparison of ORP based regulations vs FC level based regulations is misleading. They prominently mention the two cases where ORP was used as the basis for regulation, but fail to note the hundreds of jurisdictions that regulate based on FC.
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    Mod Squad jblizzle's Avatar
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    Re: We don't recommend ORP

    Quote Originally Posted by PigIron View Post
    Looks a little too "pro-ORP" to me
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    Re: We don't recommend ORP

    I should note that the active chlorine level is related to the FC/CYA ratio so measuring FC alone is not enough. However, the CYA level doesn't change very quickly so in practice having a target FC level for a given CYA level and then just maintaining that target FC is all that is needed for maintaining disinfection and reasonable oxidation rates. The absolute FC/CYA level will differ between a residential pool where algae prevention is most important to commercial/public pools where disinfection rates and higher oxidation rates are more important (though really such increased oxidation would be better coming from supplemental oxidation such as ozone).
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