Aalkalinity question

[linux]

I'm a new pool owner and am busy learning about pool chemistry and how to spend money. I think I have the basics, and that pH is important, along with TA and CH. I bought a salt system and had it installed; it seems to be working well.

My question has to do with why the alkalinity has been dropping. It went from 90 to 40 in about two weeks and the pH dropped with it (that part I understand). I bumped it back up to 70 and the pH went from 7.0 to 7.4. I'll probably add some more baking soda to get it up to 100 or so.

Anyway, the only thing I can think of is that there are a lot of pine trees around our pool (we're in Georgia) and several storms have deposited leaves, pine needles and tons of pollen in March. I tried to scoop them out, but at first I didn't realize that the water level was above the skimmer and there was lots of debris for a couple days.

Anyway, do leaves, pine needles, etc lower the Alkalinity (ie, more acidy)? Also, would (acid) rain also contribute to this as well?

Thanks