There needs to be an air gap between the roots and the nutrient. That can be accomplished by lowering your nutrient and planting deep in the pot or by adding a medium and planting higher in the pot. The important thing is the air gap be present. I start all of my seeds in rock wool with a few bits of hydro ton in the bottom as soon as the roots emerge it can go into the system. If you are running vigorous air ration the roots don't even have to touch the nutrient.

I have just posted a photo in another section, but I will post it again. The roots should not be totally submerged in the nutrient solution or they will drown, rot, and die.
Allow only about 1/4" in the bottom of the pot to have nutrient solution, as the plant grows it will throw down more roots chasing the nutrient solution and at the same time allowing oxygen to be available to the roots. Google KRATKY method of hydroponics and see the history and success growing leafy vegetables.

Thanks guys appreciate the feedback :)