Calcium hardness recently plummeted . . Why?

[JoeN64]

I test my water regularly and CH is typically in the 220 - 240 range. We had a couple inches of rain about 10 days ago, and when I tested last weekend CH was only 91. We have had a lot of rain before, but I've never seen CH drop so dramatically and so quickly. I added 10 lbs of calcium chloride over 2 days. When I tested again today the CH is still only 119. After the rain the only other parameter that was out of whack was CYA being low, which made sense.

Anyone have any idea why it would have dropped like that, and best way to get it back to normal?

TC 2.2
FC 2.2
TA 98
pH 7.8
CYA 54
CH 119
Salt 3300

Pool is clear, with no issues. TIA!

 

[Rancho Cost-a-Lotta]

How do you test your water?

 

[Bperry]

I test my water regularly and CH is typically in the 220 - 240 range. We had a couple inches of rain about 10 days ago, and when I tested last weekend CH was only 91. We have had a lot of rain before, but I've never seen CH drop so dramatically and so quickly. I added 10 lbs of calcium chloride over 2 days. When I tested again today the CH is still only 119. After the rain the only other parameter that was out of whack was CYA being low, which made sense.

Anyone have any idea why it would have dropped like that, and best way to get it back to normal?

TC 2.2
FC 2.2
TA 98
pH 7.8
CYA 54
CH 119
Salt 3300

Pool is clear, with no issues. TIA!

Pool stores and electronic meters tend to give really bad test results and is why TFP doesnt recommend ever trusting them. Get the Taylor K2006 or a TF100 kit for better accuracy.

 

[HermanTX]

I test my water regularly and CH is typically in the 220 - 240 range. We had a couple inches of rain about 10 days ago, and when I tested last weekend CH was only 91. We have had a lot of rain before, but I've never seen CH drop so dramatically and so quickly. I added 10 lbs of calcium chloride over 2 days. When I tested again today the CH is still only 119.

If you only check CH occassionally then it can appear to be a big drop but if there was considerable rain where you have an autodrain and auto refill, there is a water exchange taking place . I have seen it already this summer on my CH with the heavy rains we had in April & May.
Also, you may have some error due to testing at a pool store where contamination to previous water test, lack of training on summer employees and test apparatus is not calibrated.

On a side note, your FC is quite low for your CYA. Please see
FC/CYA Levels
At TFP this FC/CYA relationship is a cornerstone of our methodology as is using a proper test kit and do self-testing.

 

[JoeN64]

How do you test your water?

I use a combination of a Leslie's Home Accublue test, an electronic probe for salt and pH, and test strips as needed. My Taylor reagents had expired, so I have more coming this week. I test weekly, and this drop was sudden. Over 1 week. I don't have an auto drain system, so the only recent added water is rain. Thank you!

 

[Rancho Cost-a-Lotta]

The sudden drop and lack of gain in CH makes no sense. Most likely the issue is with the test results. Don't add any more CH until you refill your Taylor reagents and get some reliable test results. I think your results will be where you expect them to be.

Best wishes!