The platform that holds the plants is usually made of Styrofoam and floats directly on the nutrient solution. An air pump supplies air to the air stone that bubbles the nutrient solution and supplies oxygen to the roots of the plants. Water culture is the system of choice for growing leaf lettuce, which are fast growing water-loving plants. The one drawback with this system is that very few plants other than lettuce will do well in this type of system. The biggest drawback of this kind of system that I could find is that it doesn't work well with large or long-term plants. .
The third type of system is the Ebb and Flow system, and it works by temporarily flooding the grow tray with nutrient solution and then draining the solution back into the reservoir. This action is normally done with a submerged pump that is connected to a timer. When the timer turns the pump on nutrient solution is pumped into the grow tray. When the timer shuts the pump off the nutrient solution flows back into the reservoir. The timer is set to come on several times a day, depending on the size and type of plants, temperature and humidity and the type of growing medium used. The Ebb and Flow is a versatile system that can be used with a variety of growing mediums. The entire grow tray can be filled with gravel or granular Rockwood. Also I found that many people prefer to use individual pots filled with their choice of growing medium. This makes it easier to move plants around or move them in or out of the system. The only real problem that I found with this type of system is that with some types of growing medium (Gravel, Growrocks, Perlite), do not hold water very well, there is a vulnerability to power outages as well as pump and timer failures. If this happens the roots can dry out quickly if the watering cycles are interrupted. The only solution that I could find is to use a growing medium that holds more water, this will only give you more time to find and address the problem.
