What's causing calcium fluctuations

[joephu]

I ran my waterfall to aerate the water to bring TA from 110 down to 80 since my CYA was at 80. I kept ph at 7.0 to 7.2 to speed up the muriatic acid process of lowering TA. Boy, did my TA drop. The final number was 60 TA, calcium also drop to 240. Over the summer calcium went from 300 to mostly 400, then 420 about a week ago prior to aeration. From what I read, calcium is like CYA in that unless you're doing a water change, it shouldn't really change.

I did add in 9 boxes of Borax with Muriatic per site's instructions but I don't think that should have any effect on CH, right?

 

[jblizzle]

Has to be testing error. Nothing you did should have lower the CH.

 

[johnsimion]

I also don't understand this quote: "... I ran my waterfall to aerate the water to bring TA from 110 down to 80 ..."
As I understand the Pool School, it's the acid that is supposed to lower the TA. All the aeration does is raise the PH back up.
I can attest to the aeration raising PH, since I can add gallons of acid to my pool but the aeration from the spa spillover will raise my PH back up within a couple of hours. So quickly, in fact, that the acid doesn't even seem to have much effect on the TA.