There is some truth to synthetic nutes in hydro system being cleaner and not leaving as much heavy metals etc in the plant/flowers, but its not as easy as just running hydro. first you need a good healthy root system the plant has be able to easily intake and discharge. second its all about the feed , when the plant is through its heaviest flower weeks and is starting to come to an end you need to start eliminating the elements it doesn't need. Remember a plant will uptake some elements whether it needs them or not , it just stores it, and some elements are not very moveable with in the plant. so the amounts of these elements have to be none or at least low enough that virtually all of it will be used, otherwise your last resort is getting them out in the flush.and third is the flush , Ideally a week of just pure clean water, and changed often. This can flush out a lot of stuff out of the plant. now i know some guys say no need to flush its a waist of time, here is what I say. take some samples of a plant that has not been flushed and send it out for testing for exactly what is in it and percentages. and then do the same for one that has been properly flushed for a week, and then say it doesn't matter.Also this is hard to do with bottled or pre made nutes because your always throwing shit at your plant it doesn't need, really you need to mix your own nutes and adjust the elements as needed.