If you don't supply a food source, especially in soiless/water your bacteria will all die, but hopefully produce enzymes in the process. This scenario isn't all that bad if your in mid flower and root growth is not your primary goal, but up until then I think it's best to provide a food source to keep them alive. Once you hit mid flower you want to have want your enzymes to be breaking down old root material and any other organic elements in your medium so nutrient availability is at it max when the plant is at its peak feeding needs. . .