Actually, to lower your alk, you add acid until your pH is 7.0 (which drops your alk at the same time), then aerate your water to let the pH rise again without raising the alk.

Since CYA testing is a turbidity test, if you had anything clouding your water at the time of the test, it could give a false reading. If you haven't added any CYA yet, you definitely need to--otherwise all your chlorine is going to waste!

Janet