OK, I estimate you have 25,000 gallons, not 33,000 (16.5**2)*(3.1416)*4*7.5= 25,659 gallons. (PI*r**2*Depth*7.5)=gallons 7.5 is gallons per cubic foot. 4' is the depth of your water, not the height of the sides of your pool.
Only two ways something called "shock" will turn water green that I know of. 1) It's not chlorine 2) there's lots of metal in your water. The brown stuff on the skimmer may confirm that. The water should be checked for copper and iron, I think.
So what was the "shock" you put it? It should list the ingredient.
I'm also a bit startled that you CYA/Stabilizer went from 0 to 45. It can't happen in a few hours, and it certainly cannot happen from adding Dry Acid (That's the generic for pH Down).
Any other mods and our super experienced gang of posters, please feel free to chip in.
Carl
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