Problems with chlorine

[Johnsbd]

So, I've been noticing that my FC has been fairly low at the end of the day when we test. I tested CC and has been less than 1, and water looks good.

A few days ago I got a FC of 1.5. Called for 14 cups 10%. I tested an hour later and it was at 11FC. I double checked everything and came up with same amount of chlorine, so not sure why it jumped to 11.

Decided to test first thing in the morning and it was 9FC which would mean that I need to slam. Although the CC and color were still good.

I decided to wait a couple of days and try it again thinking something was wrong with my numbers or something.

Tonight I get a reading of 1.5, pool math says to get to a 7FC, I need 14 cups. I decided to put in 10 and retest in an hour. Came back with 6.5 FC.

I dont know know what I'm missing. I tested CYA a couple of weeks ago and it was between 30 and 40. I noticed I'm out of the agent for testing that, so I ordered some. But I'm just using liquid chlorine so I wouldn't expect it to change much.

Help! It's probably something simple that I'm missing.

Here re are my daily targets:
7FC
7.4-7.5 pH
90TA
40 CYA

Thanks, Betsy

 

[Akathisia]

Maybe your pool is smaller than 16k?

 

[Johnsbd]

No, we just put it in last summer. Sure of the size. I even double checked that though!

 

[Johnsbd]

Anyone have any ideas on what to check or do different?

 

[Jimrahbe]

Betsy,

I suspect you are using Liquid Chlorine at 12.5%... 80 oz (10 cups) will increase the FC in a 16K pool by 4.9 which is pretty close to the reading you got... (1.5 plus 5 = 6.5)

The Liquid Chlorine that I use in the winter, when my SWCG is off, is 12.5%

Thanks for posting,

Jim R.

 

[Johnsbd]

I checked. It's 10% liquid chlorine. I did get my test chemical for CYA today. I could still clearly see the black dot even at 30 CYA. So could this be the issue?

Although I'm not sure I would understand that either since the lower the cya, the lower the amount of chlorine you need. I will read up on what I need to do to get my CYA up and then figure out if I need to slam.

In the meantime, I'm still very confused on my FC levels and why adding 13 cups raises my FC by 9 instead of 5.