# Thread: CH in fill water, what is the impact on over all CH in the pool?

1. ## CH in fill water, what is the impact on over all CH in the pool?

It's been a while since I have done algebra on solutions and mixtures so here's my question:

I have a 20,000 gallon pool with CH at 300 ppm.

My fill water has 125 PPM.

If I lose 1,000 gallons due to evaporation, and fill it back up, what is the impact of the fill water?

Is there a formula for calculating this?

2. ## Re: CH in fill water, what is the impact on over all CH in the pool?

Evaporation does not remove any calcium, while topping off the pool adds additional calcium. So calcium levels just go up and up.

When adding water to replace evaporation the formula is:

Final calcium level = starting calcium level + (fill water calcium level * added gallons / total gallons)

where starting calcium level is the level from before the evaporation.

3. ## Re: CH in fill water, what is the impact on over all CH in the pool?

Right, CH doesn't evaporate, just like CYA. Is it total gallons (20,000 in my example) or where the water was at before adding (19,000 in the example)?

So with that formula, I set it up as follows (with total capacity):

300+(125*(1,000/20,000))
300+(125*0.05)
300+6.25=306.25 <--- New CH value after water is topped off

I believe that is correct.

4. ## Re: CH in fill water, what is the impact on over all CH in the pool?

Yep

Total gallons is before evaporation, as you assumed.

5. ## Re: CH in fill water, what is the impact on over all CH in the pool?

Awesome. So my fill water does not appear to have as much of an impact as I thought it would. Heck, I may lose more CH than I can replace from rain water dilution and splashout.

Thanks Jason!

6. ## Re: CH in fill water, what is the impact on over all CH in the pool?

It all depends on how much rain water gets into your pool. Some people direct it into the pool off the roof top etc.

7. ## Re: CH in fill water, what is the impact on over all CH in the pool?

Here ya go
http://jfhtm350.webs.com/pool/FillWaterCalculator.html

3rd calculator down. Made that today.

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