Many apons will go dormant after they flower. The bulbs may come back after a few weeks if they were able to absorb enough nutrients from the substrate during the dormant phase. As far as "needy" is concerned, apons definately need potassium like a previous poster mentioned, iron suppliment, good lighting, as well as regular N,K and traces. I have also found that my apons do better at a warmer temperature. When I had my temp at about 70F, the plants grew slowly. But soon after increasing the temp to 78-79, the aponogetons started growing much faster.