If you are really in week 3 , if you are growing in coco ( your infos says hydro ) and if you are using the canna nutrient lines then why aren't you feeding ATM ? I mean in coco after the 1st week you can start to bring nutreint at a ec level around 1/1.2 , at week 3 you should be around 1.2/1.4 Ec. So generally the roots stimulator can be used during week 1 to week 4 but to me it's generally useless after week 2 as you'r starting to use the "real" nutrients ( I mean the basics and importants ones )