In your pool, each quart of 6% bleach will raise your chlorine level by 1 ppm. So, if your chlorine level is 2.5, you want to add enough bleach to raise it back up to 15. The small jugs you can buy are 3 quart jugs. So, to get from 2.5 to about 15, add 12 quarts of bleach which would be 4 of the three quart jugs. It won't hurt your liner and the more consistently you can keep the cl at 15, the quicker your conversion is going to go. Don't be afraid to take the cl up to 15. That is what it is going to take!

For the bleach calc - 15,000 gallons, 6%, then quantity put .25 which would represent one fourth of a gallon which is one quart. You'll see that it will tell you that one quart will raise your cl by ppm.