OK, I found something on their website regarding water volume. According to their package labels
http://npk-industries.com/images/lab...row_Back35.jpg
And
http://npk-industries.com/images/lab...oom_Back35.jpg
It says to use 1-2 tsp per gallon of water. Therefore 2 tsp would be full strength. This confirms my suspension that a 2oz package isn't enough for 400 gallons of
nutrient solution. I'm not sure where you got that figure from, but for that to be possible that 2oz package would need to make 800 teaspoons. Or even going by the smallest amount of 1 tsp per gallon of water, that 2oz package would need to make at least 400 teaspoons (roughly 8 cups).