Pool Chemistry After Heavy Rains

[RexO]

I am a new, first-time pool owner and have been maintaining my pool for about 2 months. IChlor30 SWCG system, plus new exposed aggregate pool (plaster), so the pool is still eating plenty of acid to keep PH in range. We have heavy rain in Central FL on Memorial Day, so I tested my water first thing this morning (Taylor 2006C). As expected, alkalinity and stabilizer was down. Easy adjustments. But, I was surprised to find the PH jumped from 7.6 to 8.0 during the rainy day. I was reading that rain might lower the PH along with the alkalinity. I suppose the SWCG running all day with overcast and raining skies added to my FC (5 to 6) and helped boost the PH. Anything else going on here? Wouldn’t rain normally lower PH or at least be PH neutral?

 

[IceShadow]

The aeration on the pool surface can cause CO2 offgassing, which can cause the pH to rise, like any other aeration.

 

[IceShadow]

I always had a pH increase after rain until I got a pool cover. Then the pH went down with the rain.

 

[RexO]

The aeration on the pool surface can cause CO2 offgassing, which can cause the pH to rise, like any other aeration.

Yeah, that’s probably it. Aeration from the all-day rain and the SWCG working all day in the overcast sky, exceeding my target FC level...driving pH up.