The effect of rainwater on swimming pools

duraleigh

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#21
Yeah, I was just about to say the same thing! :shock: :shock:

Richard, I followed everything right up to that big word that began with extra....something...something.

Seriously (for just a moment), the forum is indebted to guys like you and Mark and others who can make scientific logic out of the gibberish that sometimes appears here. The net result for all of us is a better understanding of our pools and, as a result, much more enjoyment from them. :lol: :lol:
 

mas985

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May 3, 2007
12,182
Pleasanton, CA
#22
Missed the backwards formula. Didn't look quite right.

As for the measureable PH drop, could it be that the pools were measured right after the rain and did not have time to properly mix the rain water with the pool water?
 

NWMNMom

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Apr 8, 2007
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#23
duraleigh said:
Rangeball,

I'm still trying to ferret out someone that can definitively say that rain has increased their pH. It sounds like that's been your experience. How much rain over what time? How much pH rise did you get?

If you remember (or not) last May we had over 15" of rain in a very short period of some days and in fact that was the net result - higher PH. We usually run in the area of 7.2-7.5 and found ours hovering around 7.8 or higher. This was the first time we have EVER had issues with high PH.
 

Rangeball

Well-known member
May 25, 2007
785
#24
NWMNMom said:
If you remember (or not) last May we had over 15" of rain in a very short period of some days and in fact that was the net result - higher PH. We usually run in the area of 7.2-7.5 and found ours hovering around 7.8 or higher. This was the first time we have EVER had issues with high PH.
Out of curiosity, do you remember where your TA was?
 

Hotrod30

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Dec 22, 2007
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Central New York
#25
I took a PH reading on the rain that fell Tuesday. We received .45 inch of rain. The PH was about 6.6 or 6.7. I had the wife check my results. Sometimes we get some nasty rain here in central NY.
 

Nina Li

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Jun 12, 2012
98
Tampa, Florida
#26
These past few weeks, it has rained almost non-stop down here in Florida. In between the showers, I'm out there (when I'm home after work) scooping up some leaves and vacuuming to keep all that organic debris out. It's a stuggle sometimes, but so far, water is clear. I have a feeling that my luck is going to change soon..we're having more rain until Wednesday. (today is Friday!) I'd better start testing, right? yipes. :?
 

MattB

Active member
Jul 6, 2011
40
Chambana, Illinois
#28
All rain is acidic because it is in equilibrium with atmospheric CO2. The pH of "pure" water (no CaCO3 or anything else) in equilibrium with the atmosphere is 5.65. You can see the calculation here: http://ion.chem.usu.edu/~sbialkow/Class ... 0Acid.html

Obviously this fact has little to do with our buffered pools' chemistry. And I agree that the amounts of water are small compared to most of our pools and most significant changes must come from runoff into the pool.

Incidentally, my geochemist friend tell me that they really don't start talking about "acid rain" until the pH gets down to 4 or even 3, FWIW.
 

Nina Li

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Jun 12, 2012
98
Tampa, Florida
#29
We still have a tropical storm over us here in Tampa Florida (when will this rain end!!!)...but I went for a swim today anyway..the rainwater was "deliciously refreshing", lots of it... I added a little bit of bleach to my water yesterday because I saw some algae on the edges,loosened the stuff with a mop, ran my pump for about 12 hours and then "oilaaaa"..clear, clean refreshing water! wow - glad it worked. The rainwater seemed to freshen it up..so did the bleach too I think. Going in tomorrow again! More rain coming..ugh!
 

lelandapple

Well-known member
Jul 12, 2012
103
Winter Haven, FL
#30
Yeah I live in Florida, was hit by tropical storm debby hard. something like 7-8 inches I think. My pool was blue and cloudy at the time turning it from green to blue. Surprisingly, the rain and winds from the TS pushed all of the junk to the bottom and I was able to see the bottom of the pool for the first time! I was so excited as we could never see bottom until that point! Just a random bit of info, but it was neat. I didn't notice a pH diff but at that point i said i wasn't gonna worry until after the TS didn't log any information down.
 
Apr 16, 2016
12
Miami, Fl
#31
If you remember (or not) last May we had over 15" of rain in a very short period of some days and in fact that was the net result - higher PH. We usually run in the area of 7.2-7.5 and found ours hovering around 7.8 or higher. This was the first time we have EVER had issues with high PH.
I had a substantial increase of pH after several days of moderate rain in South Florida. I have a Taylor 2006 kit but get an analysis from local Pinch-a-penny whenever I go there to buy some chlorine. On May 23 Pinch a Penny analysis: TC=7.5 FC = 7.5 CC = 0, TpH = 7.5, A=160 Calcium Hardness = 275 CYA = 100 TDS = 1500
On 5/25 my analysis: FC = 3.5 CC <0.5 pH pH = 7.4 TA =150 CYA = 90-100. I added enough chlorine to raise FC to 9
Then it rained during the last couple of days -- I took the water to Pinch a Penny this morning and the analysis was: TC = 5, FC = 5, CC=0; pH = 9!!! TA = 140 Calcium Hardness = 250 CYA = 100 TDS = 1800 ppm Acid Demand = 4
They say the pH was out of scale hence they wrote 9, it could be 8. I might have some blown CaCO3 dust to raise the pH but that should have raised Ca hardness which has actually gone down a trifle but TDS has increased. TA is more or less the same!
The only reason I can think of is rain!
Any idea anyone?
 

tim5055

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May 11, 2014
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Franklin, NC
#32
I had a substantial increase of pH after several days of moderate rain in South Florida. I have a Taylor 2006 kit but get an analysis from local Pinch-a-penny whenever I go there to buy some chlorine. On May 23 Pinch a Penny analysis: TC=7.5 FC = 7.5 CC = 0, TpH = 7.5, A=160 Calcium Hardness = 275 CYA = 100 TDS = 1500
On 5/25 my analysis: FC = 3.5 CC <0.5 pH pH = 7.4 TA =150 CYA = 90-100. I added enough chlorine to raise FC to 9
Then it rained during the last couple of days -- I took the water to Pinch a Penny this morning and the analysis was: TC = 5, FC = 5, CC=0; pH = 9!!! TA = 140 Calcium Hardness = 250 CYA = 100 TDS = 1800 ppm Acid Demand = 4
They say the pH was out of scale hence they wrote 9, it could be 8. I might have some blown CaCO3 dust to raise the pH but that should have raised Ca hardness which has actually gone down a trifle but TDS has increased. TA is more or less the same!
The only reason I can think of is rain!
Any idea anyone?
Well, having lived in Miami/Ft. Laud for 30+ years I have gone through many an afternoon rain shower there. The first thing that comes to mind is aeration. Aeration raises pH, so a good south Florida storm will churn the water good.
 

duraleigh

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#33
The only reason I can think of is rain!
Have you read much of this forum? Why do you go to the pool store and wonder about their results?

Was your water well mixed before you went. If so, I think you have discovered the reliability of pool store testing.
 
Apr 16, 2016
12
Miami, Fl
#35
Order a TF100 from TFTestkits.net and when you get it tell us what your PH is. :)
I have cross checked the pool stores analysis and found them to be similar to my own testing with my Taylor 2006. The reason I get the water tested there (in addition to my testing) is to make my chemicals last longer. But I do my testing also in between store testing.
I collected this water sample when it was raining but from elbow depth -- I will be very surprised if rain water could affect pH up to that depth!
Anyway, I will analyze with my own kit tomorrow -- when it is not raining, and report. In the meantime I have added another gallon and half chlorine. CDC says that at a pH of 8, the chlorine has only 10% effectiveness-- that, and with my CYA =100, was a cause for concern!
 
Apr 16, 2016
12
Miami, Fl
#37
I checked today and we did not have any appreciable rainfall since yesterday. I had run my robot for three hours and the pump was running at 3000 rpm for 12 hours so I am sure the water is well mixed. I used my Taylor K-2006 to analyze this time. the pH is really beyond the scale which means >8. I added a little more than a gallon of 10.25% chlorine yesterday, FC is 9 ppm now. But with a pH of >8 and CYA >100, 9 ppm is no good!
 

Bama Rambler

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#38
I tried to find where the CDC said that chlorine had only a 10% effectiveness at pH 8 and couldn't find anything. Can you provide a link?

The K-2006 uses R-0004 Phenol Red for the pH test which is more prone to interference by high FC levels. So your pH may not be as high as you think.
 
Apr 16, 2016
12
Miami, Fl
#40
Neptunes,

I can find no evidence of that 10% effectiveness assertion. Can you provide a link?
Actually the efficacy is only 3% at pH >8 -- please see the bottom-most link

Here is the link 1 that says higher pH = less chlorine efficacy

http://www.cdc.gov/healthywater/pdf/swimming/resources/disinfection-team-chlorine-ph-factsheet.pdf

and here is a more specific link showing relation between pH and chlorine efficacy which claims is sourced from : NSW Health Advisory Dec 2012 (NSW = New South Wales in Australia)

and this is the original source: check Table 4.2 on Page 27 of the 96 page book:

http://www.health.nsw.gov.au/environment/Publications/Swimming-Pool-and-Spa-Advisory-doc.pdf

Hope this helps,