Also, water only enough to last a day when using soil. You want the plant to use all of the nutrient solution each day.
This does several things.
1. It keeps algea and bacteria from growing in the water. The water runs out every day, so the bad stuff won't grow.
2. Water has mass. As the water is used, the elimination of mass causes it to be replaced with oxygen. This is very good for the roots and the plant.
3. The plant will "learn" that it's nutes are at the bottom and it will create roots that feed efficiently from the bottom. This also provides good support for the plant.