In 28000 gallons, 2 quarts of 6% bleach will raise your chlorine just over 1 ppm. With a CYA of 10, you need to get it up to 15 ppm and hold it there by testing and adding more bleach 2-3 times daily, or as often as possible. Keep an eye on your CYA level, as it will begin to rise within 2-3 days but probably won't top out for about a week. As your CYA level climbs, then your shock level for chlorine will, too--see the "Best Guess Chart" stickied at the chlorine forum for the proper chlorine levels.

As for CYA at 80, the salt systems need it this high for optimum chlorine production from the cell. On pools without salt systems, most people recommend the lower CYA levels.

Janet