water level?

hey guys i have a 30g bubble setup with a water pump pumping straight to the midsection of my net pots.

But i need to know how far down i should place my water level for the roots to reach once the plants mature....
any advice?

I keep mine an inch or so from the bottom of the net pot

before roots break through the bottom, keep water level bearly touching netpots. then when roots grow wait some till theyr a bit established and start lowering it bit by bit. i like the roots to be 1/2 submerged so i lower it as they grow but i have a strong airpump to keep water bubbling very well