Heres a list of five different media that I consider suitable for hydroponics, they are listed in no particular order it is up to you to decide which one is best suited for your system.
There are two types of media organic and inorganic lets start with the inorganic growing mediums.
Builders sand can be used as long as it is no to fine as it will clog up the system and to calcareous as it will play havoc with the pH of the nutrient solution.
To determine how calcareous the sand is place a small amount in a glass and cover with an equal volume of dilute hydrochloric acid. A slight or vigorous effervescence indicates there is to much shell and not suitable for the task.
Vermiculite is a mineral belonging to the mica family. It is mined in several countries and is used mainly in the construction industry as a light weight concrete component. To be useful in the horticultural industry it must passes through a process to change its physical form.
The end result is a lightweight air filled cell like structure that has no nutritional value.
Photo by: tjmwatson
The draw back of vermiculite is that after a period of time in water it reverts back to its original flake like structure.
The biggest disadvantage of vermiculite is its pH value being alkaline and settles around 9.5 in water which is far to high for the purpose of growing plants.
It is important if you are going to purchase vermiculite for your hydroponic system to make sure it has a favorable pH.
Check the batch pH value, make sure it is below 7.5 otherwise it will have to be treated by soaking it in a solution of Mono-Ammonium Phosphate, you can obtain MAP from fertilizer companies.
Wash well after soaking this will gradually reduce the pH down to around pH 7.0.
Perlite is another mineral mined in several countries it goes through a milling process just like vermiculite and graded into particle sizes, then subjected to high temperatures in a furnace that causes the particles to expand four to twenty times the original size and air filled cavities.
Perlite is one of the ideal mediums for germinating seeds and striking cuttings as it has an almost neutral pH value in water. The only disadvantage is its tendency to turn into powder if handled roughly.
Photo by: blumenbiene
Rockwool is a product employed mainly in Europe as a growing medium and is starting to find its way through out the horticultural world.
It is manufactured by heating two elements namely limestone and coke into a molten mass then it is turned into fine filaments by spinning it in a turbine with other elements before being packed into slabs which can be cut to various sizes.The initial pH of rockwool makes it unsuitable for hydroponics however it can be conditioned to make the pH appropriate for growing plants.
Photo by: J Wynia
Check the batch pH value before you part with your hard earned cash, make sure it is below 7.5 otherwise it will have to be treated.