Diminishing Returns on CL

[pb4uswim]

I'm closing my pool and bringing my chlorine level up to SLAM level. CYA is around 70 (SWG). I added three gallons of 12.5 chlorine and the pool got up to 22FC. So the next day, I put in another gallon and I only got about 2 more PPM. Weather is chilly, no one is swimming but it is sunny so I guess that could have taken some of the increase out of the total, but I'm wondering - at high CYA, does the addition of more chlorine have diminishing effects on the FC reading? According to pool math, I should have got around 7ppm out of the additional gallon. SWG is off so it wasn't adding an CL during this time.

 

[YippeeSkippy]

Perhaps it wasn't all mixed in when you obtained your sample? How long before you tested?
Or possibly the gallon was older and weaker??

Maddie

 

[mknauss]

at high CYA, does the addition of more chlorine have diminishing effects on the FC reading?

No.
The strength of the liquid chlorine could be degraded. Or testing variances.

 

[pb4uswim]

Must have just lost more than I expected to the sun. The chlorine was all from the same case bought just a couple days ago.

Oh well, 22FC should be good for closing. I was planning on lifting the cover and dropping in another gal in October and maybe even November until the water is much colder/frozen.

Thanks.