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Thread: FC and ORP correlation... what to expect?

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    FC and ORP correlation... what to expect?

    I have a Pool Pilot Total Control that is giving me what I think are odd readings. Tech support told me to simply lower the set point... to 560. My test kit is showing 6ppm of FC with an ORP reading of 585 and pH 7.5. This with a set point of 650. Under those conditions, and I understand the relationship is quite complex, I would have expected an ORP closer to 825.

    My morning readings are typically higher than my evening readings even though my test kit tells me I have the same amount of FC. As suggested, I lowered my set point to 560 last night. When I went to bed, the ORP reading was 585. When I checked in the morning the pH was still 7.5, FC was still 6ppm, but the ORP had gone up to 615. Note that the set point was low enough that salt generator should not have come on.

    I am curious what others are using for ORP set points and also what to expect for a variation during the day. Are these reading just off the wall? Do they indicate a faulty sensor? I suspect the sensor is not the problem because I just replaced it. Admittedly, the replacement was not from Pool Pilot, though I was seeing nearly the same behavior with original sensor. This weekend I plan to go back to the original and take some more notes.

    Any comments on the day to day workings of these things would be appreciated. My experience is limited to my uses of this unit last season while it was functioning perfectly. (and yes, the sensors have been cleaned and stored properly)

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    JasonLion's Avatar
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    Re: FC and ORP correlation... what to expect?

    ORP readings are very sensitive to the CYA level. If your CYA level is above 50 you are going to need to lower it. With any CYA in the water it is extremely unlikely you will ever be able to get an ORP reading of 850. ORP readings are also lower in sunlight then they are in the dark, typically by 20 or 30. ORP readings also vary from sensor to sensor and over the life of the sensor.

    Typically, you adjust the water to where you want it and then set the ORP set point to whatever the ORP reading is at that time. This may need to be adjusted for the day/night difference, depending on when most of your pump run time is.
    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

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    Re: FC and ORP correlation... what to expect?

    Thanks JasonLion,

    CYA could explain what I am seeing. Last season I ran without any. I have a 20,000-ish gallon pool but am running an SC-60 so I figured it could handle the demand. It did. This year I decided to switch camps and went with 30ppm CYA at the start of the season. It's lower now due to rain (lots of rain). Of course, the manual says CYA should be 30-50ppm for the Total Control and 60-80 otherwise... to make matters worse, tech support told me I needed 60ppm minimum regardless of the system or cell size. I think I'll skip that bit of advice for now.

    So from what you are saying, it sounds like the range I am seeing is not unreasonable and so long as I can find a set point that keeps my FC at a reasonable level I really shouldnt care what the value is.

    Do you have any thoughts on gold vs platinum ORP probes? A suggestion was made that my replacement probe might be platinum while the Pool Pilot ships with gold.

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    JasonLion's Avatar
    Join Date
    May 2007
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    Silver Spring, MD
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    Re: FC and ORP correlation... what to expect?

    Gold is supposed to be a little more reliable at SWG salt levels. I am not sure how much of a difference it really makes.
    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

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