Calcium measurement mystery?

[Mdragger88]

Perhaps your pool volume is off, you purchased less potent calcium chloride or calcium chloride dihydrate.

 

[Davegnh]

We've had a lot of rain in the Northeast this summer and I've had to drain my pool quite a bit. I tested my calcium 4 days ago and it was 325. I was targeting 450 so I added 10 lb of calcium chloride. I then tested two days later and it was up to 375. Okay I thought plus or minus one drop maybe I was lower than I thought the first time. So I added another 10 lb waited 2 days and measured 400. Each 10 lb should add about 100 ppm to the pool. Check the date of the test chemicals and all good for another 8 months or more. I did double check today and got the same number twice. Is there anything that can screw up this test? I've been using the 10 ML sample that I always do.

Thanks

 

[Davegnh]

Volume is pretty close I had pool filled by pool tanker trucks. It took less than two deliveries of 6,000 gallons. Plus the little amount our garden hosed added.

I did break open a new bag of calcium chloride (ice melt from Lowes). I've used this brand previously without issue.

Other additions of chemicals have been pretty accurate. I also had to add some additional salt and adding 40 lb of salt raised my salt level accurately.

 

[Mdragger88]

Check the ingredients label- they change things all the time.
At any rate ch of 350 or 400 is plenty fine.

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[Davegnh]

My ph aways kicks up fast so try to stay in the 400s for calcium to maintain CSI under -.3 In either case just found this measurement after adding the calcium chloride very strange.

 

[Mdragger88]

The more ch you add the higher your csi goes.

 

[Davegnh]

Yep with my chemistry and temps with calcium in the 300's CSI often rides in the -.6 to -.5 I try to stay in the -.3 to 0 range in the summer.

 

[Davegnh]

In the end I had to add 30 lb of calcium to get my target 450 parts per million. Just doesn't make any sense to me.