Why did pH drop over winter?

[Saturn94]

I was discussing with friends my spring opening in progress and the question came up about why my pool's pH drops during the winter.

Normally when I close in early October the pH is at 7.5. When I open in early May the pH is usually 7.0 - 7.2.

Despite being covered with a solid cover (actually solid tarp style cover over a mesh safety cover), there is a bit of dirt, debris, and lots of dead worms/bugs (yuck!)/etc in the pool when I open.

My theory is the decomposition process of organic matter in the pool is lowering the pH. Am I on the right track, or is something else going on?

I don't see this as a problem, just curious and want to learn.

 

[Saturn94]

Another thought....

It's not unusual for me to lose some CYA over the winter. Could the biodegrading of CYA result in the pH drop?

 

[Texas Splash]

CYA can certainly drop some over the winter months and not unusual. pH changes depend on the type of pool and a variety of factors. While pH might tend to rise in colder weather, we know a newly plastered pool will accentuate that rise. Pools that receive rain water might see a drop in pH and TA. Covered pools are also effected by the entrapment of moisture and outgassing as well. If TA experiences a drop over time, it could then allow the pH to drop with it as well. Really not sure if the biodegrading of organic material would be responsible for significant changes in pH. Perhaps one of the others here might have more info in their mental (pool) tackle box.

 

[Saturn94]

Still hoping for more on this....