start bloom nutes with pre fert.soil?

[jash]

plants in week 3 flowering now-repoted 2 weeks ago in pre fert.soilmix 14-16-18 written that should last for 4-6weeks,no other nutes added.just bought bloom nutes(biobloom 2-6-3,5) but im not sure about start feeding with..im affraid that could burn them,for example i thing that soil's very high N is delaying flowering to 1 of 3 plants at the point that buds 2 nodes down of main tip are a bit bigger of a prefl.female n4 was delaying to sex so moved out..the other 2 plants in closet are buding normally.should i wait another week to start nutes or start tomorow with 1/4 or even 1/8 strength?