In order to reduce CYA, I replaced 2/3 of my pool (in one time) with tap water.
PoolSchool says "If you have algae, or the CC level is above 0.5, or the free chlorine (FC) level is zero, you should shock the pool. Many people also like to shock the pool when the FC level falls significantly, as it often does after a major storm or large swim party."
Before replacing water, FC 4-5, CYA 100-110
After, FC 0, CYA 40-50.
Then I bring FC up to 5 by Clorox.
In my case, do I need to shock my pool?
Another question, suppose I have to shock, after
"A:CC is 0.5 or lower; B:An overnight FC loss test shows a loss of 1.0 ppm or less; C:And the water is clear."
is there anything else need to do to lower FC, or just let it go down by itself?