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
30% Poly:
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.
Look here it will give you an ideal of what your getting from looking at the msds sheets:
http://jfhtm350.webs.com/pool/msds.html
Also to give you an idea of the best price:
http://jfhtm350.webs.com/pool/ChemicalCostCalculator.html
Poly is almost at the bottom.