Effects of rain on pool chemistry?

[savdoc2]

What are the effects of rain on pool chemistry?

I have read posts where people justify large FC loss due to rain overnight. Other than dilution, how will rain effect the FC levels?

I know that rain can make pH rise due to aeration, but will it have any other effect?

I know it should dilute Alk, CH and CYA, anything else to be aware of?

We received 5 inches of rain overnight and I have backwashed out about an inch. I think I will vacuum to waste tomorrow to drain it lower.

[Watermom]

Rain can also cause pH to drop if it is acid rain. If a lot of debris is blown into the pool with a storm, that can cause a drop in chlorine levels. Other than these things and those that you mentioned, I think we've got possible effects covered.

[Manslick]

I’ve had a lot of rain this year and to my surprise my levels are staying in the pocket.

Just keep testing and adjust as required.

[kelemvor]

I got 8 inches since last Thursday and it hasn't made a significant impact on chemistry that I've noticed. I'm on swcg, though. I was kind of wishing the "acid rain" would drive my pH down so I didn't have to go out in the rain today and pour acid in.

It's been so dry here this year that I've had to add water regularly due to splashout and evaporation. The overfilling of the pool by the rain is welcome here. I won't have to tell the kids to take it easy on cannonballs for a little while!

Edit: I just checked salt levels and they're down 200ppm. I'm guessing it's just because of all the extra water and the concentration will increase as water evaporates; although if it keeps raining I'll be loosing salt due to water overflowing and spilling out.

[AnnaK]

We can get some very severe downpours here in PA with 3" overnight not unusual. The only effect I've ever noticed from rain is more water in the pool. If it was a particularly 'dirty' storm, i.e., if the winds driving it carried a lot of dust, I may have dust and debris in the water. I have not noticed a change in the values for FC, TA, or pH and don't do anything special or different after even a week of heavy rains.

[CarlD]

I tend to see FC go down..but I have an automatic overflow system to prevent the pool from getting to high. Dilution is clearly possible.

Carl