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Thread: Does high pH really block out your chlorine?

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    LL Pool J's Avatar
    Join Date
    Sep 2014

    Does high pH really block out your chlorine?

    I keep reading this in articles/guides from the pool industry (even the manual for my chlorinator) but has anyone actually experienced this first hand? I assume it happens when you let your ph go above 8 for an extended period?

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    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Tucson, AZ

    Re: Does high pH really block out your chlorine?

    Welcome to TFP!!!

    No. pH has nothing to so with protecting the chlorine from the sun. Cyanuric acid (CYA/stabilizer) protects the chlorine from the sun.

    High pH is not good because it increases the risks of scaling both in the pool and in the SWG cell.
    Jason, TFP Moderator
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  3. Back To Top    #3

    Join Date
    Mar 2007
    San Rafael, CA USA

    Re: Does high pH really block out your chlorine?

    I think what they mean is that at higher pH the active chlorine (hypochlorous acid) level is lower. Though that is true, it is far less true with Cyanuric Acid (CYA) in the water. As shown in the graphs in this post when the pH goes from 7.5 to 8.0 the active chlorine drops by about 50% if there is no CYA in the water, but with CYA in the water it drops by only about 15%.
    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"

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    Join Date
    Jul 2012
    Central Texas

    Re: Does high pH really block out your chlorine?

    I've never figured out that second graph (Chlorine Usage from UV at different levels). It seems to state that the higher the CYA level, the more the loss from UV, which seems exactly backwards as to why you put in CYA in the first place.
    Central TX / 12K GAL / IG / SWG / DE filter / Pentair SVRS & 3 swim jet pumps / Spa bench and jets / Single body of water / No heater.

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