Not to be too mathimatical, but I'll give you the formula because I am not sure what concentration of the pool peroxide is. If it is not 30%, you can subsitute the percentage in. Here goes:

Use the formula C1*V1= C2*V2 where C = concentration and V = volume.

So if you need one quart (32 ounces) of the store bought (3%) peroxide to make up a gallon and assuming that the pool concentrated peroxide is 30%, you would use the following:

.3(= to concentrate pool peroxide percentage of 30%) * V1 (the unknown amount)= .03 (desired concetration perocide percentage--3%) * 32 ou. (1 quart what you would use of the store bought normal peroxide)
or
.3*V1= .03 * 32 ou

reduce to
V1 = .03 *32 ou / .3

do the math and you'll get:

V1 = 3.2 ounces of concetrated 30% pool peroxide in one gallon of homebrew scent killer. Of course this is assuming that the pool peroxide is really 30 %.

Now aren't you gladthat you asked?