I had my pool perfectly balanced then left for vacation after the 4th and the person who was supposed to take of it couldn't. We shocked with the same amount, when we returned and used in the Spring with no show of Cl the next morning. Bought new Cl, 12% bleach, and added, again the same amount used in the Spring and according to pool.calculator., with no show of Cl, again. Could the bleach in the bottles sold to us be old? How can I test the cl in the bottle?