I think that much flushing in hydro is hurting potential yields. My final week, I'll scale back the nutes, add PK boosters and sweeteners, and allow my plants to drink up that res water. Each day I top off the res with plain water and pH adjust. By the end of the week, I've probably replaced 10 gallons out of a 15 gallon res with plain water and I consider that my flush. I usually change my res every week but I'll usually let them go 10 days on that final res change which pretty much tapers them off nutes and on to plain water. I don't get a harsh product nor does it smell like nutes. That's my approach and it works for me, but 10 days of flushing is too much for hydro, IMO.