Another method is to put the dry ice into a Styrofoam container with holes in it to slow down the rate of evaporation. Since carbon dioxide is heavier than air it must be placed above the plants in order for it to drift down and surround the plants. Fermentation is another way to create more carbon dioxide in your hydroponic greenhouse. Hydroponics is proven to have several advantages over regular soil gardening. The growth rate on a hydroponic plant is 30 to 50% faster than a soil plant that was grown under the same conditions. The yield of the plant is also greater. There are many reasons for the drastic differences between hydroponic and soil plants. Hydroponics is always a soil less culture, but not all soil less cultures are considered to be hydroponics. Many of these cultures do not use the nutrient solutions, which are required for hydroponics. 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 first thing any hydroponic gardener needs is a dedicated area for their gardening. Most newbie gardeners can either purchase an easy to install grow room or build a greenhouse outside of their home. Small grow rooms for the beginning hydroponic gardener are usually slightly larger than a closet and can be completely installed in under an hour. 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. The pH level for plants determines what type of nutrient solution that they need. Acid loving plants need a pH level below 7 while other plants need a level above 7 to achieve optimal growth. In addition, for optimal absorption of the nutrient solution, air must be allowed to circulate around the roots of the plants.