You won't need the Fusion for a tank that small and not keeping high demand coral like SPS and Clams. Fusion is a calcium and carbonate dosing product. This can be accomplished easily in 12 gallons with a good water change schedule. Don't waste your money on the Fusion.
FYI filter floss does not make nitrates. The nitrogen cycle does. Filter floss traps suspended particles from the water and if left in the tank and not changed regularly will become an area where;
1. Said particles will be trapped and will over time start to degrade into ammonia.
2. Nitrifying bacteria will start to populate the floss as it is a source of food.
3. The bacteria will do their job in breaking down the ammonia into nitrites and the nitrites into nitrates. As their are no anaerobic (thrive in areas of little to no oxygen) bacteria to finish breaking down the nitrates into nitrogen gas you get an increase in nitrates in the tank.
So the floss really needs just to be changed 2-3 times per week to avoid this. And the floss, as it removes the suspended particles, helps to avoid any water clarity problems caused by suspended particles and to remove the source of some of the larger proteins that cause nitrates problems with nitrates.
As you can see I believe floss to one of the better - inexpensive things an aquarist can use to help to maintain water quality.
JMO