The choice of growth mediums for your hydroponic tomatoes is an important factor in the success or failure of your attempts. Since there is no soil involve in hydroponics, one must choose between Heydite, Perlite, clay pellets, vermiculite, and Rockwool.
You need to look for a medium solution that is close to PH neutral, give enough support for the plants, keep and hold moisture, and give space for a good air exchange.
To determine which medium is best for your application, you need to look at what type of plants you plan on growing, what type of water systems in use and cost. For continuous drip systems a course media such as clay pellets will work best. They are also best for larger plants and can be used over and over.
Rockwool is popular choice because it provides small plants with a good balance of water and oxygen. It can also be used for continuous drip or flood and drain type systems. Usually, rockwool is only used once, so the cost in larger systems can become problematic.
Whatever growth medium you choose needs to be thought out ahead of time and planned to provide a successful opportunity for you hydroponic tomatoes.