Over and over, I see posts where the OP blames a recent rain for disturbing the balance of his/her pool water. I don't understand how this thinking gets started because I don't see a cause for it.
1. If you have an AG pool, Obviously nothing but rain gets into it during a storm. Assuming you AG is 4 feet deep and you get a huge 2" of rain, you have only altered the pool water by 4%......hardly enough to make any measurable difference in anyone's pool
2. If you have an IG pool where the decking is sloped properly, (and the vast, vast majority of them are) you are in exactly the same situation as 1. above.
3. If you have an IG where the decking is improperly sloped and you get water running into your pool, then all bets are off and I can see how organics can contaminate the pool........but this is a tiny percentage of our pools.
So, am I missing something? Acid rain? Well, of course it exists but remember, if you get a normal rainfall, it is only a small percentage of your pool water.
"Yeah, but what if I get 18" of rain?". Of course, that will change your pool a lot but common sense should tell you there are not that many 18" rainfalls here in the US and you should probably consider moving if you experience them frequently
My point is this......I don't think we should use rainfall as a reason for our pool chemistry being altered. If there are some reasons I have overlooked that you think account for a significant change, please post them up.