I used bio bizz for almost 10 years and i always flushed like a week of two before harvest,but honestly i've not flushed with bio as well and didn't see any real difference.Bio bizz is good stuff.They claim that its 100% organic,but i think the grow isn't as i've burned my plants with it before and any true organic nute that won't happen.I'm using bio canna now and i think you could feed a whole gallon of nute and nothing would happen.