the guy at the hydro store told me not to use S.T for flowering because they have too much hormones or a certain hormone that can interrrupt with budding. I used S.T for veg from begging veg to end veg.

I've read that some ppl used it all the way from veg to flower, i've never read some that stop at veg.

you should flush with the same pH u feed your plant with.