CH Test - Instructions

[sixfive34]

I'm not sure if this is semantics or important but I noticed a difference between the provided/printed instructions and their video.
The written shows Fill to 10ml, 10 drops r10, 3 drops r11, then r12 one at a time.
The video shows Fill to 25ml, 20 drops r10, 5 drops r11, then r12 one at a time.
I know the ratios differences (increasing water by 2.5x, but r10 by only 2x and r11 1.6x) are fractional but since the amounts are so small, a fractional difference seems like it could matter.

Is one of these more accurate? Unless this is a 'close enough' test, one of these should be 'wrong', right? I know that I'd use more chemicals doing the 25ml method but I didn't make much of a dent on them last year and just ordered the replacement set.

 

[Msch99]

25ml is more accurate, but 10ml is sufficient for our needs. If your target is 5ppm, it doesnt matter much whether your test is 5.5 or 6.

 

[Texas Splash]

We typically use the 10ml water sample as noted on the Calcium Hardness - Trouble Free Pool page. It's fine for most pools. The 25 ml sample is best suited for owners who believe their CH might be very low. There are also other methods of adding drops that apply to pools who may have metals interference. But I suspect the 10 ml water sample size will work just fine.

 

[YippeeSkippy]

I learned to do the test back when 25mL was the recommended level. I still do it this way, but the 10mL would in fact suit my needs just fine. And the 10mL sample saves on reagents.

But alas, I am just a creature of habit.

Maddie

 

[sixfive34]

Thank you, all, for the replies and guidance!

 

[Richard320]

When you're testing CH in the 800+ range, you'll fully appreciate the 25 ml sample. Do I really care if it's 810, or 825?