Knifegil hate to bust your bubble but its only a deal if you get the dry form the liquide is more then prime.
32 oz. bottle treats 6,400 gallons.
You would need 640ml of prime so one 500ml 11.99 and one 250ml 7.49 so 19.48 and you are now treating 7500 gallons for.
Or look at it like this
32oz - 946ml
1litter of prime is 10,000 gallons of water.
Now look at the math for the dry
6.99 for 8 oz of dry treats 48,000 gallons it would take 4800ml of prime or roughly 1.2 gallons which is close to 70.00.
So you paid 18 and get 6400 gallons where 14.00 would get you two 8oz dry and give you 96,000 gallons or 19 dollars would have given you 2lbs and 192,000 gallons
Edit
6400 gallons for 18.00 is 0.28 cents a gallon or abouts
7500 gallons for 19.48 is 0.25 cents a gallon or abouts