You want at least 15% to 20% run-off out of the bottom of the growing container when you water. That means you need 15% to 20% of what you put in the top of the container to flow out of the bottom of the container every time you water. If you do not get good nutrient run off out of the bottom of the container then you will get nutrient lock-up. Nutrient lock-up means that the old unused nutrients have built up in the Hydroponic Growing Medium (anything other then potting soil) and/or soil to the point that new nutrients can not be absorbed by the roots. The plant will start to show signs of nutrient deficiencies, the roots will become damaged, and the yield will suffer.