You are going to have to add N. The whole concept of flushing and then starting over again with nutes is flawed and very dangerous on your plant. You are starving your plant when flushing, leaching everything out of your soil, thereby stressing your plant greatly and reducing your future yield. The best advice I can give to you is to feed your plant by watching it daily, notice a lightening of the leaves especially the bottom leaves. Keep your leaves green throughout the grow and the yield will follow. No need to flush in soil, seriously doubt in hydro or other methods but other topic. The taste and smoothness will be gain upon proper drying and curing, but you need a healthy plant to start with.
edit: Almost forgot, welcome to RIU I hope you find it informative and entertaining. Word of warning on accepting advice: look at their grow journal, does their info make sense, do lots of searching and reading on your own........google is your friend. Devote a portion of your day to reading on growing, just like you spend time watching your plants, it will pay you great dividends. Just my two cents.
I wish you luck in your grow.
but ya... like canefan mentioned, no one likes going on diets (neither does ur plants).. im not here to debate "flushing" --that topic attracts trolls n flamers