why with 10 higher than with 25 and how does CH decline?

[engrav]

CH is now tending low so I will start adding in increments but two questions please

1) If I test with 10ml sample I get 275, with 25ml sample I get 230. I guess the difference is not really relevant since both are kinda low but why the difference? Or is this really no difference?

2) A month ago with 10ml sample I got 325. Maybe this difference is really no difference but say it is. How might CH decline save by splash out (which I have little) and replace with water with low CH?

Testing with TF-100
FC 4.5
pH 7.6
TA 90
CYA 30-40
CH in well water used to replace evaporation is 90 or 100.
Splash out essentially none.
Pool is not leaking.

 

[pooldv]

Is your pool plaster or vinyl?

CH only goes down with splash out, drain or overflow. Or rain. Or if the pool is scaling and depositing calcium scale on the pool walls. What is your CSI in PoolMath? Has your oh or TA been higher in the past?

More detailed testing instructions here, Pool School - Extended Test Kit Directions

 

[engrav]

ah yes, winter / spring rains
went back in the pool diary and found I add Ca every season after winter / spring rains and the back wash to restore the level (pool is not closed in the winter)
interesting, will expect it next year
thank you