hi bdt 1981,
yes I do
but also made at least one run without ( well with a flush before harvest ).
So you can but don't have to
Run for 4 weeks, take a sample out of the res and compare ( just visual ) to a sample of new nute !
You may also experience a rise in Ec which would force a flush.
I know guys doing that every week ! but if you have a big res you will throw away a lot of nutes, not good.
so you could,
- when you switch to flower ( if you veg for 2-4 weeks, or every month )
- after 4 weeks ( maybe you'll add some booster here )
- after 2 weeks ( you want to remove booster now, affects taste )
- before harvest.
Have a nice day !
edit :
forget ph'd water and atazyme ( or whateverzyme of course ).