If your CYA is 40, then 12-14 isn't high enough to reach shock level. You need to get it up to 15 and keep it there until the pool clears. You said that on day 2 or 3 you started to notice the water quality changing, and said that the chlorine was "good"--was it at least 5? With that CYA, once you get the pool clear and your cl drifts back down, don't let it go past 5 or you'll have another algae bloom. Also, when you notice the water quality changing, it won't ever hurt to shock it--but you need to test it to analyze what the problem is. That's how you keep from just dumping a bunch of stuff in it hoping to fix the problem--you usually create more problems for yourself that way than you fix.

Shock the pool, hold it at shock level, brush it daily, keep your filter running 24/7, and it will clear up.

Janet