Clear water Slam day 11?!

[pooldiy]

Day 11 of slam. Not sure if I’m missing something. Water has been clear all along but loses 3 ppm overnight.
Brushing daily, shut off swcg 1 hr before checking at night for OCLT and morning test 15 min before sunrise. What else to do?
CYA 40
Using slam shock chlorine level of 16. Testing/adding chlorine every 4 hrs during day, It’s been between 16-37 each test. CC 0
Usually run 20% swcg but have it at 100% plus adding liquid bleach when needed for slam
Realize 40 cya is low for swcg, should I add cya?
Also ph was 7.2 before slam
TA 60
CH 250

 

[JoyfulNoise]

Have you deep cleaned the sand filter?

 

[pooldiy]

Thank you! No, just backwashing. Worried that will create more issues or Problems with filter ?
Is there a time recommendation for deep cleaning? Not sure it’s ever been deep cleaned. Pressure is fine. Hasn’t been above 25% of normal

 

[JoyfulNoise]

If it’s never been deep cleaned then it should be. You could just have junk built up in the filter that backwashing will not remove (backwashing is inefficient at cleaning out fine embedded matter). So it could be a source of chlorine loss.

 

[IceShadow]

We opened our filter and found probably 5-10 lbs of pine needles that wouldn’t be able to backwash out a month or so ago.

 

[IceShadow]

Be sure you’ve checked your steps, ladder, light niches, etc. Those can hide algae.