I see frequent posts wherein folks have attributed their pool water chemistry being out of whack because of rainfall.......I tend to disagree. I have been incorrect before and will be so again but here is my thinking:
Let's assume you get three inches of rain
Your pool averages 48" in depth
Let's also assume you have an AG pool or an IG pool that does not get surface water running back into it. If you're getting surface water, all bets are off and you need some landscaping ASAP.
Let's also assume that your pool before the rain was balanced perfectly...something like this:
FC - 4.0
CC - 0.5
TC - 4.5
pH - 7.4
Alk - 90
CH - 200
CYA - 50
OK, what does the rain change?
Chlorine? Not really. You got a 6% increase in your pool water so that means your TC is now 94% of it's former value....(3.76ppm)
CYA? Nope. Your CYA dropped from 50 to 47ppm....immeasurable.
CH - Exactly the same dilution....you now have 188ppm
"Okay, then, how about pH and Alk, Dave?", you're asking, "Don't you know squat about acid rain?"
Well, I can't do that logrhythmic math but it's been discussed here before and I can tell you your pH moves very little. Subsequently, your Alk will move very little as well.
What this adds up to in my mind is that many of us put w-a-a-a-y to much emphasis on rainfall's ability to dramatically alter pool chemistry.........What's your opinion?