CYA fluctuation

[lkalred]

New pool owner, first summer.

Have experienced CYA fluctuation with rain dilution, evaporation in N Texas heat calls for refilling often, resulting in CYA fluctuation. CH also going down with dilution. Was advised earlier that rain should have no effect on chem levels. How is it possible to get significant dilution and have no change in chems?
Is this a product of my testing techniques or is this normal? Forecast calls for multiple inches of rain in next few days. Maybe this is just the result of owning a pool in TX. Should I expect to have to add CYA? Again?

Todays numbers:

FC-6.5
CC-.5
ph-7.3
TA-50
CH-340
CYA-50 (was 40, added 2 lbs 3 days ago)

Water is clear to the point of can tell heads or tails on dime in deep end. Thank you TFP!

Thanks

 

[duraleigh]

The water in your pool evaporates but the CH and CYA do not. Once you refill, those two parameters return to normal.

Rainfall does dilute them but not nearly as much as many people think. A 48" deep pool that gets 2" of rain dilutes by 4%, etc.

 

[JohnN]

The only way rain can make it go down is if the pool gets to the point of overflowing. But it would take a lot of overflow to make a noticeable effect.

 

[harleysilo]

If you are draining water from your pool you will be draining out some CYA and Ca.