There are lots of ways the pool industry tries to move money from your bank account to theirs.

I'm a believer that non-chlorine shocks are one of them, as are most algaecides.

In the fall before closing, I boost my FC to ensure I have no CC, then add a quart of polyquat algaecide (the only one we recommend here). I wait 48 hours then boost my FC up to the shock level for my CYA (stabilizer) level and close.

All I do all winter is syphon out some water if it gets too high. I've yet to have algae in the spring...so watch, this year will be the first time ...but not yet. I just checked yesterday and the water was clear, despite having a surprisingly mild fall and winter.