I get an average of about 60" of rain per year. My pool is probably an average of about 5-6' deep. Does that mean that most of the water in the pool is being replaced by rain every year?
What does "inches of rain" tell you about how much rain water goes in your pool?
- Thread starter TomAtlanta
- Start date
- May 23, 2015
- 25,705
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
Precipitation is measured in a linear rate scale such that the collection area doesn’t matter. So yes, your pools volume is changing by inches of water level. If you know your pools surface area, then you can calculate how many gallons of water you get in a rainstorm. 1 cubic foot of water is 7.48 gallons (US).
- May 23, 2015
- 25,705
- Pool Size
- 16000
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- Pentair Intellichlor IC-60
For example, Tucson has an annual average evaporation of 95-100” of water per year. That means almost my entire pool volume evaporates in one year. Before my pool autofill was hooked up to our water softener, my CH would increase annually by 200-250ppm. That’s almost exactly how hard my municipal fill water is.
My pool gains three inches for every inch of rain. But then, I have a gutter downspout feeding the pool. 
Actually, the three inches is only when it's pointed that way. I usually let the first day of a big storm bypass so it washes off the roof and I don't get so much dirt in.
In your case, you don't replace all the water every year because the rain water mixes with pool water before it leaves. So if your pool was 50 inches average and the storms came through and dumped 2" each time, you'd lose 8% of CH. and then the next time 8% of that and so on Grab the calculator. .92 *.92 * .92 and so on 13 times (more than the whole volume of the pool) you'd still have over 33% of the original.
Actually, the three inches is only when it's pointed that way. I usually let the first day of a big storm bypass so it washes off the roof and I don't get so much dirt in.
In your case, you don't replace all the water every year because the rain water mixes with pool water before it leaves. So if your pool was 50 inches average and the storms came through and dumped 2" each time, you'd lose 8% of CH. and then the next time 8% of that and so on Grab the calculator. .92 *.92 * .92 and so on 13 times (more than the whole volume of the pool) you'd still have over 33% of the original.
That explains why the level of stabilizer and hardness goes down slowly over time. I have been using a combination of trichlor tabs, cal hypo shock, and liquid bleach to keep stabilizer and hardness balanced. I figured out through trial and error that that worked.
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