Hello chip.
I use it like this,
weeks 1 - 3 = 2ml per ltr.
Weeks 4 - 7 = 3ml per ltr.
I then stop feeding b h for the last 2 weeks of bloom. If your plants flower for longer than 9 weeks stay on 3ml per ltr for the extra week or weeks.
It does cost a few bob but it does cover its cost easy! I buy the £40 ltr bottle a lot better value for ya money.
Good luck mate.
hantshaze.....