The data I have so far is uncomfortably soft. I have the Taylor phosphate kit.

From the initial supply bought from Amazon in June, I used about (not measured, guessed) one and a half quarts to get from > 1000ppb to 500ppb. At this point, I added 5 days worth of bleach, covered the pool and went on vacation.

Ten days later I uncovered the pool, FC 12ppm (CYA 60), some appearance of what might be dirt or might be mustard algae in the seams and corners where it usually grows. Allowed FC to come down and maintained 5.5ppm-7.5ppm FC. Added about 1/2 the remainder of the second quart.

Another ten days or so go by with several thunderstorms bringing tree debris into the pool. Definite return of mustard algae. Brush, vacuum, backflush. PO4 now at 250ppb. No makeup water for the three weeks since PO4 measured 500ppb. Added the remainder of the second quart.

So, about 8oz of the (June) Kem-Tek phosphate remover took about 250ppb out of my 7700gal pool. If my math is right, that's a whole lot more like 0.75ppm/10,000gal than 2.0ppm/10,000gal as described on the label. This is of course confounded by the storms, debris, high chlorine and time.