Yes it need's light nute's,thats it's only source of food.
Yea that's the right amount of nute's (atleast according to GH).I change my water every 2 weeks or so,but in DWC i would prolly go with weekly.Stale water can cause root rot.You might ask some of our DWC guy's about that.Try to get a ppm meter,it's worth the cost.