Hi im new in Hydro and I think Im buying something like thishttp://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=130383217973&ru=http://shop.ebay.com:80/%3F_from%3DR40%26_trksid%3Dm570%26_nkw%3D130383217973%26_fvi%3D1&_rdc=1#ht_703wt_1165. it will be inside a growing tent. my question is how does hydro works, I know that you dont need to use any soil and that it is all water and nutes. My question is, the hydro sistem needs to be always on with the water runing or what, and the other question is, what type of nutes it used?