There is no such thing as 'chlorine lock.'

As far as people having algae issues after rain, it is typically because they don't go out and check their pool during the rain and thus their chlorine level gets too low.

Take a look at the Best Guess Chlorine Chart in my signature below if you haven't already done so. With a CYA of 50, you never want your chlorine to drop below 3. So, even if it is raining, get out there and keep the chlorine levels up!