Overnight loss 0.5-1ppm. water is cloudy. black dirt. Can i stop shocking?

[nikon5400]

I started adding CYA when pool was covered, on Tuesday. Had the sock in until Wednesday.
Removed cover last night (Saturday), around 8pm with CYA about 20-25 with new sock in to bring CYA at around 30.
Brought PH down to about 7.2-7.4
Didn't test anything else..
Added 3 gallons of 12.5% which brought chlorine level to 15.5 (about 3 qt more than needed. Either the chart changed or I forgot how much chlorine I used prior years)
8-9 hours later 14.5 (29 drops of 0871)

Water is still cloudy.
Cartridges are old, overdue for replacement. I guess it'll take a bit longer to clear.

I'd like to know if I should still keep chlorine at the shock level or not.

Also, this time I have this black dirt I don't remember ever seeing before. It comes off relatively easy with brush. What could it be? I had like a dozen places like on these pictures

Thanks

 

[mknauss]

SLAM Process article has three criteria for being successful. The first is crystal clear water.

Maintain your SLAM level FC by testing and adding liquid chlorine every few hours. Brush the pool, all surfaces, as often as possible.

Once the water is crystal clear, run an OCLT.

 

[nikon5400]

Thanks. My water is crystal clear as of Sunday night! Overnight chlorine loss has been 0.5-1ppm every night
(To be honest, I didn't keep shocking, so my 15.5 ppm from Saturday night turned into 3.5 ppm Monday night, with lots of sun both days and temperature up to 90 and up to 80 and water temperature from low 60s to 69. I may have wasted 1 gallon by bringing it up to 15.5 ppm by mistake. (instead of 10-12ppm) )

I believe this is 2nd or 3rd season in a row when my pool has no chlorine loss at opening. The only difference is the way I've been closing it lately - I cover it first when it's too cold to swim, but keep the pump running and after a few weeks, when the temperature drops to around 60 I finish closing. I don't use algaecide, don't even shock, just close it with ~2ppm FC
Maybe this closing routine helps, maybe coincidence, but it seems to be working for me and saves me lots of headache and chlorine during opening.

One thing I think is worth doing at opening - adjusting CYA level while pool is covered, so no extra chlorine is lost to sun after removing cover. I assume CYA of is ineffective until it's fully registered, 7 days after adding.
I don't know if adding chlorine while pool is covered is a good idea as I was told chlorine is damaging cover.

Please let me know if I'm wrong on my closing or opening routine.

Thanks.

P.S. Also, I'm happy to learn that my 14m old liquid chlorine lasts longer than I anticipated