Your pool water should get very cold for your location. The poly 60 isn't really needed. Just bring your FC up to shock level for your CYA level before you close. Open early when water temp is in the 50's and your water should be clear an algae free.
I've never used the poly, just bring my FC up to shock level and all is good. I open early. 😎
Dimethyl benzyl ammonium chlorides are Quatanery Algaecides and not the same. There are no sources for Polyquats near me either so I would have to order online to have it but I dont use them. If I knew for some reason I was going to run out of FC then I would use some.
Here are some brands to get you going. 60% Poly:
Aqua Guard Algaecide 60% Concentrated
BioGuard Inhibit Algae All 60
Clorox Pool and Spa Concentrated Algaecide
GLB Algimycin 600
HDX Algaecide 60% Concentrate
Kem Tek 60% Algaecide Concentrate
Omni Multi-Purpose Algaecide 60
Poolife Super AlgaeBomb 60 Algaecide
Pool Pals 6-0 Poly Algaecide
ProGuard 60% Algicide
ProTeam Polyquat 60
Sun Non Foaming Algaecide 60
Aqua Guard Green Algaecide
GLB Algimycin 3000
GLB Algae X
Kem Tek Green Algaecide
Poolife AlgaeBomb 30
Pool Pals 3-0 Poly Algaecide
There are also some other lower percentage products but 60% is usually the best deal.