Hey bizzy-

If you are 5 weeks in, I am guessing you mean, changing over the nutes and not flushing... Flushing is done in the very last weeks before you harvest the plant. It is just giving the plant plain old water to rid the roots of the chemicals and not making your smoke taste nasty. If you meant changing the nutes and putting new nutes with new water in, then yes, I would clean out your system at least every 2 weeks. I usually do it every Sunday, but that is just me...

Good luck...