im a soil grower but im shure after you feed that food stays in you res i get well water so i fill up 3 5 gal buckets with water when i get home i nute one up with full strength nutes and then dilute it with reguler water so i can change the strenght i can have 1/2 recomended nutes or 1/4 if i wanted but the nutes stay in the res the whole 2 weeks it last me i think your supposed to change you water every 2 weeks for hydro so once there is food in the water there is no need on feeding agin unless you want to raise from like 1/4 strength to lik 3/4 strength