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Thread: Does Rain Alter Pool Water Chemistry?

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    Does Rain Alter Pool Water Chemistry?

    Over and over, I see posts where the OP blames a recent rain for disturbing the balance of his/her pool water. I don't understand how this thinking gets started because I don't see a cause for it.

    1. If you have an AG pool, Obviously nothing but rain gets into it during a storm. Assuming you AG is 4 feet deep and you get a huge 2" of rain, you have only altered the pool water by 4%......hardly enough to make any measurable difference in anyone's pool

    2. If you have an IG pool where the decking is sloped properly, (and the vast, vast majority of them are) you are in exactly the same situation as 1. above.

    3. If you have an IG where the decking is improperly sloped and you get water running into your pool, then all bets are off and I can see how organics can contaminate the pool........but this is a tiny percentage of our pools.

    So, am I missing something? Acid rain? Well, of course it exists but remember, if you get a normal rainfall, it is only a small percentage of your pool water.

    "Yeah, but what if I get 18" of rain?". Of course, that will change your pool a lot but common sense should tell you there are not that many 18" rainfalls here in the US and you should probably consider moving if you experience them frequently

    My point is this......I don't think we should use rainfall as a reason for our pool chemistry being altered. If there are some reasons I have overlooked that you think account for a significant change, please post them up.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Does Rain Alter Pool Water Chemistry?

    Dave,
    You need to spend a summer in Florida and see what rain is during "Monsoon season". (That's not an invitation unless you want to be the poolboy all summer! )When you get about 2-3" an hour and winds of 35 MPH on an average rain just about daily(and often it's more severe such as the 2 hour thunderstorms we had at the beginning of this last week) it can have an impact on pool water even with a screen room over it! I usually have to bump up my FC at bit after a rain like that because it's dropped (or I crank up my SWG and keep my FC a bit higher during the rainy season to compensate. I have seen changes in pH after a heavy rain. I do not know the cause but I have seen it happen and I know it's no testing error! My deck is sloped properly and has proper drainage but when the rain comes down so hard that there is up to a foot of water in the streets because it cannot drain fast enough ti's also gonna have an effect on a pool!

    As far as moving....NO WAY. I LOVE my house on the beach.

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    Casey's Avatar
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    Re: Does Rain Alter Pool Water Chemistry?

    Hi duraleigh.

    We have had a rainy, rainy June in my neck of the woods of beautiful SW PA. Although I agree with your post for the most part, I think all this stinkin rain has taken a toll on my CYA level.

    I opened at the end of March this year and I'm sure you remember how crystal clear my pool was. My only issue with opening was nearly nill CYA when I believe it was 40-50ppm when I closed in September. Here is the the thread I posted about.

    I bumped my CYA level up to 40 and was running there pretty consistanly until this month, my chlorine seemed to be burning off at max speed so I checked the CYA and it was considerably lower and I feel it's because we have been pounded with rain. My pool has over flowed through the skimmer several times this month alone from all the rain.

    The only thing I really have had to add to my pool so far is the CYA, Borax and Baking Soda in the beginning when DH took the cover off and I dose regualarly with GV 6% bleach, usually daily while checking pH and TA regularly along the way with the CYA. So basically, I'm just adding bleach. *Pretty simple if you ask me*

    I have found, for the most part that my PH and TA have hung in there but my CYA is running on the low side and the only thing I feel I can contribute it to is all the excess rain and over flowing of the skimmer. *shrug*

    Here are my latest test results after filtering for atleast a half hour from it setting all night with the solar cover.

    FC 5.5 <added 2 nights ago>
    TC 5.5
    pH 7.5
    TA 90 <changed at 8 drops but turned nice and pink at 9 drops>
    CYA 28 <estimated>
    Temp 72* <don't laugh people! I'm trying! hence $100 solar cover purchase>

    What gives? Is it because of rain/overflow?
    I'd bet you my bikini you'll never get TFP water from a pool store!

    24' Sharkline Venture De Filter

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    Re: Does Rain Alter Pool Water Chemistry?

    Evan,

    From the National Weather Service Climatalogical Data for St Augustine FL...

    Average annual rainfall is 47.42 inches

    Dryest month is April with 2.63"
    Wettest is Sept with 6.45

    Prime swim season months are....

    May - 3.11
    June - 5.27
    Jul - 4.5
    Aug - 5.91

    It's hard for me to find a consistent "monsoon" season in there and it's hard for me to find much evidence of the 2-3"/hour rainfall that you refer to.

    I fly in and out of Florida almost monthly. It can certainly rain quite hard for brief periods of time but the Florida rainfall data is not exceedingly different from NC (We get 45" average in Raleigh (that's from memory....not exact)) or much of the Southeast.

    I will certainly believe that catastophic rainfall events can and do alter anyone's pool water.....a hurricane is a perfect example. Day in and day out, I do not believe normal daily rainfall has much effect.

    Casey, I do believe that short-term climatological variations can certainly alter CH, CYA, probably even pH. That's over several days or weeks and that's not the thought behind my discussion.

    My idea is that a one-time thunderstorm has little effect. A month of rainfall double what is normal or having an overflowing pool many times in a month can be a 50% exchange of pool water and that will certainly alter your pool. I am looking for valid arguments that one-time heavy rainfall events alter pool chemistry with any significance.

    The change in your CYA is certainly valid given that so much of your pool water has been replaced.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Does Rain Alter Pool Water Chemistry?

    Dave, I have lived in Florida just about all my life. Even up here in St Auguutine my pool is only not swimmable for about 2 months out of the year! I use my hot tub during those months. Not arguing with you but my experience is that rain does have an effect on pools (and it's not just me, my customers saw the same thing.)

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    Re: Does Rain Alter Pool Water Chemistry?

    We've had 2-3" per hour rains here in my part of PA recently which have measurably affected the pH of my pool water.
    — AnnaK —

    12,000 gal AGP, Hayward sand filter, Pentair 2-speed pump, timer.
    Please visit our Pool Issues pages for information about step weights, managing the solar cover, and PoolSkim.

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    Re: Does Rain Alter Pool Water Chemistry?

    Quote Originally Posted by AnnaK
    We've had 2-3" per hour rains here in my part of PA recently which have measurably affected the pH of my pool water.
    exactly!
    I just tested my pool since this the first day this week it has not rained (YET) and my water balance is totally off...salt, cya, and borates low, pH low (but nothing I can't live with, and chlorine low. The pool was perfect last week.

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    Re: Does Rain Alter Pool Water Chemistry?

    exactly!
    I just tested my pool since this the first day this week it has not rained (YET) and my water balance is totally off...salt, cya, and borates low, pH low (but nothing I can't live with, and chlorine low. The pool was perfect last week.
    I don't understand this post.

    Are you saying you now have to add salt, CYA, borates and chlorine as a result of a weeks worth of rain?

    If your pool averages 4 feet in depth and you received 6" of rain this week, that should have changed your numbers by about 12%. How much rain did you get? How low did the salt and CYA get?
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Does Rain Alter Pool Water Chemistry?

    Quote Originally Posted by duraleigh
    exactly!
    I just tested my pool since this the first day this week it has not rained (YET) and my water balance is totally off...salt, cya, and borates low, pH low (but nothing I can't live with, and chlorine low. The pool was perfect last week.
    I don't understand this post.

    Are you saying you now have to add salt, CYA, borates and chlorine as a result of a weeks worth of rain?

    If your pool averages 4 feet in depth and you received 6" of rain this week, that should have changed your numbers by about 12%. How much rain did you get? How low did the salt and CYA get?
    Can't tell you how many inches of rain I got since my rain gauge is broken but I live half a block from the Atlantic Ocean and about 3 houses away from the Intercoastal and we have had a LOT of rain lately.
    Last week my salt was at 3200 ppm today it's at 2600 ppm by digital readout and I had a low salt condition so I had to add some. The low salt may be why the chlorine was low (the unit does not generate when in a low salt condition) or it may have been from dilution. Can't really tell. Thats a 600 ppm change and that would be about a 19% change . CYA is down from 80 ppm to between 60 and 70 and that is also about a 20% change. Borates from 50 to about 40...also about a 20% change. pH is at 7,4 was about 7.7 .
    Water level in pool is up several inches but I also suspect that they hydrostat relief valve may have opened and let in ground water because the ground was soaked with water and there has been a lot of dirt on the pool this past week.

    Also realize that my total gallonage of pool and spa is less than 7k gallons. a few inches of water is a LOT of water in my pool!

    Your pool is 25 x 54. If that is rectangular with a 4 ft average depth that is almost 40k gallons. If it is a 24 round 54 high, once again with a 4 ft water depth you have about 14K gal. In both cases a few inches of water will have much less effect on your overall pool chemistry, particularly the first!

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    Re: Does Rain Alter Pool Water Chemistry?

    In both cases a few inches of water will have much less effect on your overall pool chemistry, particularly the first!
    Nope. If the average depth is roughly the same (say 4.25 feet, which mine is) then 2" of water in my pool is 4%. 2" of rain in your pool is 4% as well.

    If our average depths were drastically different, say if one of us had a diving end, that would have an influence but surprisingly, not much. A pool averaging 6 feet deep (that would have to be a pretty big diving end) would still experience a 3% change in the water volume from a 2" rain.

    So, if your CYA and borates were diminished 20% from dilution, you must have exchanged about 9 inches of pool water for fresh water.....is that correct? (I'm assuming average depth of 4 feet.)
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Does Rain Alter Pool Water Chemistry?

    Quote Originally Posted by duraleigh

    So, if your CYA and borates were diminished 20% from dilution, you must have exchanged about 9 inches of pool water for fresh water.....is that correct? (I'm assuming average depth of 4 feet.)
    Very possibly. There has been about that much water on some of the flooded roads by me.

    It is what it is.

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    reebok's Avatar
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    Re: Does Rain Alter Pool Water Chemistry?

    can this get moved to chemistry 201?
    16x32 21,000 gallon in-ground exposed aggregate, 1.5hp pump, 120 sqft catridge filter, birdcage, solar panels, aquavac tigershark qc robot.

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    Re: Does Rain Alter Pool Water Chemistry?

    Quote Originally Posted by reebok
    can this get moved to chemistry 201?
    Done!

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    Re: Does Rain Alter Pool Water Chemistry?

    It may be worth mentioning that Florida has been in a drought for something like the last six years. You can watch here as it all gets pretty much wiped out during late May. We had a LOT of rain.
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

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    Re: Does Rain Alter Pool Water Chemistry?

    Quote Originally Posted by Ohm_Boy
    It may be worth mentioning that Florida has been in a drought for something like the last six years. You can watch here as it all gets pretty much wiped out during late May. We had a LOT of rain.
    AND as anyone who has ever lived in Florida can attest to we sometimes get very localized pockets of heavy rain! I have seen on more than one occasion the sun shining and no clouds across the street from me while I was in a torrential downpour!

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    Re: Does Rain Alter Pool Water Chemistry?

    "Had a lot of rain" also probably means

    - pool may have overflowed some, dillution of chems?
    - got a lot of leaves blown in on the wind, plus dust and pollen, consumes FC?
    - lots more aeration due to rainfall, pH rise?
    - possible acidity of rain, pH fall?

    When it rains here, mostly I get debris in the pool from nearby trees. Some washing in from my own landscaping on the back side and the rocks around the pool tend to have some dust and plant material in the nooks and crannies that is not a problem at normal water levels but when the pool is near to overflowing all that ends up in the pool. It takes some time for the Polaris to catch up and for me to empty the skimmers and in that time I lose a lot of FC.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: Does Rain Alter Pool Water Chemistry?

    I know that when I first put my SWG pool in, I tried to keep the CYA and FC on the very low side - and had a lot of problems with rain "upsets". Now that I keep my CYA within the proper range (based on the numerous discussions on this board and PB about how SWGs function much better when the CYA is kept in the proper range as specified by the manufacturer), I find that I have much less rain related problems. I think my pool was "on the edge" and lots of rain and blown in material could easily push it over. Now that my pool is solidly "in the middle" chemistry-wise, rain seems to have much less effect.

    Except for having to continually pump out all of the stupid June rain we have had this year in the NE!!
    20 x 40 vinyl IG. SWG. Solar. Ikeric VS pump.

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