How much chlorine for a drain/fill/slam?

[mepot101]

I am going to do a major drain and fill this weekend, my current cya is over 120. (too many pucks)

Any ideas as to how much chlorine i am going to need? Probably going to go with pool store liquid at this point, getting 2- 2.5 gal jugs tomorrow, want to be prepared before I start.

 

[mknauss]

Hard to tell. Start with 20 gallons and go from there.