Not holding chlorine during the day

[Talental]

Hey guys, new to the forum as well as my pool.
The pool was finished last August. Standard 20x40 vinyl liner pool with a salt water generator.
I purchased the Taylor test kit recommended on this site. I have done my due diligence but am stumped on my chlorine levels.
I am doing a SLAM but having a real hard time holding my chlorine level during the day.
The water looks great. It’s clear and I have passed the over night test twice.
First time went from 10.5 to 10
Last night. 8 and stayed at 8.
My problem is I will check the chlorine at 0600 and it’s 10. But by lunch it’s dropped to 4.
I currently have 0 CYA.
My current theory is the sun is just burning off all my chlorine. It recieves full sun most of the day.
What are yalls thoughts?

 

[mknauss]

Welcome to the forum!
For a SLAM you need at least 30 ppm CYA. The half life of chlorine with 0 CYA is less than an hour with sun shining on the pool water surface.

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I suggest you read ABC's of Pool Water Chemistry and consider reviewing the entire Pool School eBook.

 

[Richard320]

You have it figured correctly.

With no CYA, it's amazing the chlorine lasts even til lunch. You need to raise that to 30 CYA or better.

Also, if you passed OCLT, the water is sparkling, and no CC, you're done. So rebalance everything, which includes CYA.

I would add only 30 ppm and check again in a week. You might have 15 or 20 CYA already, and you don;t want to overshoot. Its easy to add more later if it turns out you had none.