Acid Rain

Just for giggles I tested pH on the rain collected in my rain gauge (Thunder storm last night).

It was < 6.8 using K-2006 kit. I ran the "Base Demand" and got 9 drops before I was able to compare to pH 7.6 on the comparator. I wonder how low it actually was??

No wonder the pool pH dropped!! (.73" rain = ~350 gallons added to the pool) (the solar cover was on so there was no aeration rise).

I think the pH of "normal" rain is somewhere in the 4.0-5.0 range; "acid" rain is marginally lower. But, as chemgeek explained here or over on troublefreepool.com, rain is a weak acid and therefore doesn't have the pH lowering effect you might think it would. As you implied, it actually raises pH in many instances because of the aeration it provides.