that soil is fine. you should eventually flush yes. even if your whole grow goes smooth at the end 2 weeks or so prior to harvest you wanna flush like mad to remove all the horseshit from your plants. all you have to do is flood the pots with 3x the volume of soil in it. its easy.
you may have to flush before if you screw things up... i hope you dont. it really sucks to see your plants suffer.