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Thread: Increased water conductivity with oxidation

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    benavidescj's Avatar
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    Increased water conductivity with oxidation

    Will oxidizing organics produce ions that would increase the conductivity of the water? I did a little research that had anecdotal evidence of this. Just wanted to know if anybody had ever run across the answer.
    Carlos
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    Re: Increased water conductivity with oxidation

    It certainly could but not a lot and if the oxidized material is in solution as opposed to in suspension.

    Scott
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    Re: Increased water conductivity with oxidation

    The vast majority of ions in the water that contribute to conductivity come from two sources. First is the initial set of salts that are added to the water including additions of calcium chloride to raise Calcium Hardness (CH) and any sodium bicarbonate to raise Total Alkalinity (TA) (and borates if those are used, though this is mostly boric acid which is neutral and does not increase conductivity). For saltwater chlorine generator (SWG) pools, there is the large amount of additional sodium chloride salt that is added (usually around 3000 ppm).

    Second, chlorine increases the sodium chloride salt level over time. For every 10 ppm FC added by chlorinating liquid or bleach, it also increases salt by around 17 ppm. Note that with an SWG system there is no net change in salt because the chloride is converted to chlorine and then gets used up to become chloride again so any change is due to dilution from splash-out, backwashing, rain overflow, etc.

    As for oxidized ammonia and organics, they roughly fall into two main categories. First are organics that may not get oxidized at all or may only get partially oxidized but that are generally insoluble such as most suntan lotions and some other oils. These get caught in the filter and removed from the pool. Second are ammonia and urea which is the largest component of sweat and urine. These mostly get fully oxidized to nitrogen gas and carbon dioxide gas though there is some nitrate ion that is built up as well. Essentially, there is little build up of ions beyond that from the chlorine that becomes chloride when oxidizing such organics. Other organics may get partially oxidized and build up to some degree remaining dissolved. Urea itself, as well as N-chlorourea, are neutral molecules and do not increase conductivity of the water. However, these quantities pale in comparison to the rising salt levels from continued chlorine usage (except for SWG as noted above). In outdoor residential pools, the majority of chlorine usage and therefore salt buildup is from breakdown from the UV in sunlight.

    Countering this trend towards increasing salt levels and conductivity is water dilution.
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    Re: Increased water conductivity with oxidation

    Richard,

    how about muriatic acid (MA) impact on increasing salt level & conductivity with a SWCG ?

    I've been tracking a couple pools, my own included, where we started from about 3800 ppm and since everything is automated, there are no "manual add-ons" of any chemicals or substances.

    Salt levels have climbed in both pools to 4350-4450 ppm with IC40 cell flashing high salt (but still producing normal).

    MA is slowly injected into the line as pH stays at 7.5-7.6

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    Re: Increased water conductivity with oxidation

    Muriatic Acid does indeed increase the salt level since it adds hydrochloric acid which is hydrogen ions and chloride ions. Probably the easiest way to track this is related to the amount of acid that lowers the TA by 10 ppm which is 25-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons. This also increases the salt (chloride measured as ppm sodium chloride) by 7.1 ppm.
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    Re: Increased water conductivity with oxidation

    Quote Originally Posted by susa
    I've been tracking a couple pools, my own included, where we started from about 3800 ppm and since everything is automated, there are no "manual add-ons" of any chemicals or substances.

    Salt levels have climbed in both pools to 4350-4450 ppm with IC40 cell flashing high salt (but still producing normal).
    Water added to the pool to replace water lost to evaporation will increase the salt level.

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    Re: Increased water conductivity with oxidation

    Quote Originally Posted by JamesW
    Water added to the pool to replace water lost to evaporation will increase the salt level.
    Good point. I forgot about that. I usually don't think of it because normally fill water is low in salt. It's usually calcium that is more of a concern for increasing Calcium Hardness (CH). Nevertheless, if the fill water has significant sodium chloride in it, then the chloride level will increase in the pool with evaporation/refill.
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    Re: Increased water conductivity with oxidation

    Quote Originally Posted by JamesW
    Water added to the pool to replace water lost to evaporation will increase the salt level.
    I would think the opposite to be true. Adding water that contains no salt should not increase the salt content of the pool. The perceived salt content of the pool as viewed by the SWG should decrease since the salt water is being diluted by the fresh water.
    Carlos
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    Re: Increased water conductivity with oxidation

    The fill water will never be completely salt free. The salt levels of fill water will typically be quite low, unless it is coming out of a water softener, but almost never zero.

    You also need to take the complete evaporation/refill cycle into account. As water evaporates no salt is lost. If exactly the amount that evaporates is replaced with new water the salt level goes back to exactly what it was to start with, plus any salt contained in the fill water.

    Salt goes down from backwashing and splash out, as the salt concentration in the lost pool water will essentially always be higher than the salt concentration in the replacement water.
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