Watch your parameters REAL carefully, as this is a small tank, and that would be A LOT of food. What exactly do you have in there? I would not feed all that in a 12 g nano! If this is the advice of your LFS, I would say they managed to do what they wanted, which is get you to buy 4 bottles and use it so that you will need it replaced soon.
That is a feeding rate, IMO, for a tank pretty heavily stocked with filter feeders. Even then (assuming you have no skimmer) it is a lot.
In the future, I would buy something more significant.