Large CH Drop

[FLPoolDIY]

My CH has been constant at 300 until this week. I tested my water today and had a drop of 156 ppm. Background info: I test everything once a week, FC and ph daily. We had about 2 inches of rain and the water temp is 59 F.

What could cause the large drop in CH?

Today's test results:
FC - 9.5
CC - 0
Ph - 7.7
TA - 90
CH - 144
CYA - 75
Temp - 59F
Salt - 3600
CSI - .63 high because of low water temp

 

[Texas Splash]

Good evening. CH shouldn't drop drastically unless there is a significant water exchange. I'm curious about your CH result of 144. When we test CH, we use a multiplier of 25 x the number of drops (until blue) to get the CH. I would expect to see 125, 150, 175, 200, etc. Can you clarify how you obtained 144? It may help us a bit.

Pool School - Extended Test Kit Directions

 

[FLPoolDIY]

I must have been distracted when doing the test. Good catch! I'll retest in the morning and report back. Thanks for the reply.

 

[duraleigh]

You may not have mixed the pool water thoroughly with that new rain water prior to taking the sample.

 

[FLPoolDIY]

Retested this morning CH 325. Not sure how I came up with the 144...
All is good now. Thanks for the replies.

 

[Texas Splash]

Ahhhhhhhh. Much better.