The basic items you need after you decide on either a grow room or greenhouse include a temperature control unit, exhaust fan, heating mats, light fixtures for your blue and red spectrum lights, an aeration system (an aquarium system works well for small gardens), pearlite, marble and Styrofoam work well as a beginning medium and rockwool, oasis or Rapid Rooters. Hydroponic plants are entirely water based which makes it possible to fully automate the hydroponics system. Specially formulated hydroponic fertilizer mixtures are required and should be tested after dilution to ensure a pH level of between five and six. This nutrient solution should be changed every two weeks and in between changes should be checked so the volume is kept level by adding more water only and not additional formula. In addition, for optimal absorption of the nutrient solution, air must be allowed to circulate around the roots of the plants. Plants that are constantly waterlogged will not thrive and their leaves will eventually fall off. Nutrient solutions can be made by the home gardener or purchased pre-mixed from a variety of sources. Some of the more popular water culture systems include raft systems, nutrient film techniques, and aeroponics. Hydroponic gardening requires an energy source in order to grow. Usually, natural sunlight is used, but during the shorter and darker days of winter, many hydroponic gardeners use artificial lights to increase the intensity of light or to expand the daylight length. There are two main types of hydroponics, which are solution culture and medium culture. Solution culture uses a nutrient solution but does not use a solid growing medium for the roots. The medium culture has a solid growing medium for the roots such as gravel, sand or a perlite culture. Hydroponic plants are grown in a number of ways, each supplying nutrient solution to the plants one way or another. As both small and large hydroponic farms were established in the late 1970s, it was proven that hydroponic culture could produce premium produce and be a profitable venture. As hydroponics attracted more growers, complete plant nutrient formulas, and hydroponic greenhouse systems were being marketed.