Seahunt Posted June 30, 2011 Report Share Posted June 30, 2011 I live in MD. Have a 22K gallon plaster pool (10 years old). I use liquid bleach so the PH tends to drift up. Tested the water and PH is at 7.8. Go in the shed and I am out of liquid acid so I put it on the shopping list for tomorrow. We have a rainstorm that night and the next day I go to put the acid in and test the water and the PH is at 7.2. Wow, the rain dropped the PH that much! Don't remember rain affecting PH that much in the past. I wonder if our rain is getting more acidic? Just curious. Quote Link to comment Share on other sites More sharing options...
chem geek Posted June 30, 2011 Report Share Posted June 30, 2011 That is strange. The aeration from rain drops sometimes has the pH rise from carbon dioxide outgassing, but even acid rain shouldn't lower the pH of the pool unless there was a LOT of rain. The reason is that the pool water is buffered while the rain is mostly not (except for some carbon dioxide from air). So usually the amount of acid in rain isn't enough to affect the pool pH. Nevertheless, this is what you saw so I'm baffled by this. As shown in this link, the pH of normal rain is acidic at around 5.6 while acid rain might be down to 4.2. If I assume that there was 3" of rain and average pool depth is 4.5 feet (54") then I can start with pure water and add carbon dioxide to it to get to a pH of 5.4 and sulfuric acid to get the pH down to 4.2. If the pool TA is 80 ppm, then this results in the pH dropping from 7.5 to 7.36 so I suppose that with sufficiently acidic rain in large quantities that the pH could drop, but your drop was rather large. Are you reaching down 1 foot or more below the water surface to take your sample? Maybe your earlier high reading was near the surface and after the rain the water got churned up so that you then were reading a more average value. The pH near the surface of still water will be higher due to the carbon dioxide outgassing. Quote Link to comment Share on other sites More sharing options...
Seahunt Posted June 30, 2011 Author Report Share Posted June 30, 2011 I usually try to reach down arms length to get a sample. I guess one data point does not prove or disprove a hypothesis. I'll keep an eye on the weather and run another test. I thought that drop was huge. Thanks for the feedback. Quote Link to comment Share on other sites More sharing options...
AFiremanFirst Posted July 3, 2011 Report Share Posted July 3, 2011 How close are you to an airport? I'm right in the flight path of DFW airport, sounds crazy, but we hardly notice the planes, except when they weren't flying post 9/11! anyhow. the jet fuel is dumped over us, and no, of course it doesn't rain down on us, but it does end up in our rain, and it affects our pH. Go outside and look at your gutters, if they are streaked (and it will be obvious) then you have a little jet fuel affecting your pH, no big deal, just keep an eye on it! Quote Link to comment Share on other sites More sharing options...
Seahunt Posted July 13, 2011 Author Report Share Posted July 13, 2011 Well, must have been bad reading on my part. A couple more rainstorms and not a huge drop as I indicated. Thought it was weird. Thanks for the feedback. Oh, and on the flight path, that is interesting. The planes to BWI airport do go over our house. I haven't noticed the streaks on the gutters but boy is it on the white fiberglass boats at the marina! Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.