CYA is lower than expected

[johig]

Since my pool was filled (December 2019) I have been gradually raising the CYA. The pool guy started out with chlorine pucks when it was too cold for the SWG to run. After startup was complete, I began adding solid CYA a couple of pounds at a time using the sock method. I am up to a total of 10.5 lbs of CYA added to approximately 17,000 gallons over about 6 months, but I'm reading my CYA test at around 50 ppm maximum. Some days I swear I can still see the black dot at closer to 40 ppm. Based on pool math, I was expecting the reading to be higher by now. Is there anything I'm missing here? I really don't want to add too much CYA. I'm topping up the pool regularly due to evaporation, but I am not backwashing or doing anything that causes a lot of water to be lost from the pool. Any suggestions on what is happening here? I suppose I could take a sample of my water to the local pool store and see what they come back with on the CYA test. Thanks in advance for any insight you can provide!

 

[tim5055]

Well, if your pool is 17,000 gallons then 10.5 pounds of stabilizer should raise the CYA to 73. Each puck used would have been additional 2 CYA

We generally see a natural decay of maybe 2 CYA a month, so that may be 10 or so less

If the pool is a littel larger than 17,000 and with the margin of error in the test you are getting close, but still 10-20 off.

 

[johig]

Well, if your pool is 17,000 gallons then 10.5 pounds of stabilizer should raise the CYA to 73. Each puck used would have been additional 2 CYA

We generally see a natural decay of maybe 2 CYA a month, so that may be 10 or so less

If the pool is a littel larger than 17,000 and with the margin of error in the test you are getting close, but still 10-20 off.

Thanks! This is reassuring. My volume might be a bit larger than 17,000. I try to keep it conservative in Pool Math to make sure I don't add excess chemicals.

 

[Richard320]

Did you ever get enough rain at any one time to make you empty some water? I know we had a couple storms a bit north of you where I had to empty about 4" out before the next storm, and another couple after that. 6" is 10% of my water.

 

[johig]

Did you ever get enough rain at any one time to make you empty some water? I know we had a couple storms a bit north of you where I had to empty about 4" out before the next storm, and another couple after that. 6" is 10% of my water.

This could be it, too. We did have some decent rain storms and that would have sent some water out of the overflow.