This video discusses water volume and feed input to determine the concentration of nutrients. There is a misconception that the total amount of nutrients in a system determines the availability of nutrients. This is simply not true. Plants require nutrients to be delivered in concentrations (water volume + total nutrients) to effectively take up nutrients.
If you were to increase the water volume and neglect to proportionally increase the nutrient input then your system will run lower on nutrient availability to plants.
Watch the video to get the full breakdown