My own personal rule-of-thumb is that Polyquat should be under $20/quart for me to buy it, unless I'm desperate.

All the pool stores sell it in this area, (NJ), including the biggies like Branch Brook, Leslies, National Pool, as well as the single store shops. Remember: It could be called ANYTHING like Mustard Algae controller or Black Algaecide--I look at the ingredients for the 60% Poly....<something> and ignore the label.

When it's on sale I'll buy several quarts--it doesn't go bad in a cool, dark basement.

It's amazing the literal crud pool stores will sell you that mess up your pool. Like selling you poison as "nutrients".

When you see "Double-acting Stabilized Chlorine", beware--the second actor is....COPPER.

Copper's great stuff. Goes good in pennies (better than zinc), nickels (75% copper), electrical wire, roof flashing, certain cookware, and other decorative stuff. But it's lousy for pool water.