This is the best description I found:Wilma Hydro Organic Systems - Growing Systems
Wilma Hydro Organic Systems
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SKU# G235

"Thanks to an ingenious re-circulating drip-based design thatâ??s capable of accommodating any type of growing medium, you can expect to achieve fantastic results courtesy of a Wilma System whether using pebbles, rockwool, soil or coco! Each system comes supplied with all the different drip stakes you need, so if after a few crops you fancy changing the growing media â?? you quite simply can! Moveable pots and handy pot location pins on the top tray make the Wilma System incredibly flexible and enable you to quickly and easily reposition plants for uniform crop growth. What's more, you've now got the option of growing larger plants in 3 new BIG Wilma Systems that accommodate 18 Litre pots. These are available in 4, 8 and 9 plant versions."
Well its a shame they dont include a decent instruction booklet on even the basics of working the system with different Mediums because surely they cant expect everyone to know everything.