Lynn, don't feel stupid, I'm sure no one is born knowing what polyquat is. Poly quat is short for an impossibly long name of the active ingredient (and the only active ingredient on the label). The 60 in 'poly 60' stands for 60% (of the poly quat), this diffences it from poly 30 or poly 10 (30% and 10% respectively). Some of the other algicides use amonia (and other stuff) or copper, it's always a good idea to check the active ingredients.
The folks here say to only use the poly 60 however, I say that if you can get a better deal on poly 30 (the cost of 2 qts poly 30 < cost of 1 qt poly 60) buy the poly 30, but add both quarts. The forum regularly advocates comarison shopping on bleach (comparing the chlorine % to the cost per bottle and amount per bottle) to insure that you get the most for your dollar. I say apply the same to algicide, if you should somehow luck into a 12 qt case of poly 5 being less than a quart of poly 60, buy the case and use it all to do the same job as the 1 qt of poly 60. To the best of my knowledge the 'inert' ingredient in any poly is ... water, & maybe a little coloring.
I hope I've explained this well, if not someone else will come along and clarify.
Welcome to the forum and congrats on running BBB sucessfully!! If ever you need help, don't hesitate to ask - "The only stupid question is the one unasked!" - Waste