Unless I have a murky green pool (that did happen, once) I never add large amounts of any chemicals all at once. Not bleach, not CYA, not acid. I split them into 2 doses. Add 1/2, run the pump and wait for an hour or so, test, recalculate based on the test. Then I add 3/4 of what the Pool Calc says.
Each system is unique. Pool Calc is right on for a static system and I couldn't live without it, but tweaks of its numbers are okay to do.