Yep, It's Great for Shock

put in 4.5 lbs...That should bring your Cl to 25ppm.

Now you need to keep it there. I would test again tonight and add 1 lb for every 5ppm you need to raise your Cl to get it back to 25ppm.

If you run out of Cal Hypo, use 1.5 gallons of 6% Clorox to raise your pool 5ppm.