Calcium hardness decreasing?

[yardoasis]

Today I tested CH, and it was 275... while I like that number, it's down from 300-325 from a month ago.

A bit of background - this is a new pool/plaster, and I've been working through a scaling/gray mottling problem (thread here) and trying to get the PB to come and take a look (but that's another post for later).

What I've been doing is keeping CSI under 0 as much as possible, by keeping the ph under 7.6 and TA at 70-80. Is it normal for a new pool to see CH decrease over time, or is that specific to my keeping CSI on the negative side? Or is it just due to a lot of rain in the past month? My CYA has stayed the same, or even increased a little (now 50, previously 45).

 

[JasonLion]

The only common thing that should lower the CH level is water replacement/overflow, which would also lower the CYA level. It is possible for calcium scaling to cause CH to go down, but your levels aren't anywhere near scaling conditions.

On the other hand, having test results vary by +-1 drop is fairly normal. If you are doing the CH test by steps of 25, this might just be the normal fluctuation in the test results.

 

[Richard320]

The only way CH can drop is test error, rainwater dilution, or coming out of suspension and clinging to the walls as scale.

Since you're monitoring CSI, the last option is out. One way to check would be to test CYA. IF CH dropped, so did CYA, by the same percentage. Whether you can catch that small a change with the CYA test is doubtful, though.

 

[yardoasis]

Since CYA didn't change, and CSI is low, I'll just chalk this up to regular testing variability/error. Good to understand what's going on, me being an analytical guy. Thanks guys!