1 pound of chlorine gas is equivalent to 15.3 cups of 12.5% (trade) chlorinating liquid or 31.1 cups of 6% (weight; 5.7% available chlorine) bleach.

I doubt that you are adding 6 ppm FC every day -- that is your target number, not your usage number. Your usage may be about half that, or 3 ppm FC. For your 30,000 gallon pool, that would require about 23.3 cups of 6% bleach which is the same as 12 ounces of chlorine gas. That's 12/(16*1.45) = 52% on-time assuming their numbers are correct and that your true FC requirement is 3 ppm per day.

Richard