Im finding with my Ebb and Flow that nute burn happens very easily. I was using lucas formula in RW/ Hydroton netted pots..but I couldn't stand the roots coming out of the planter. So then I switched to RW in a bed of Hydroton.
This changed everything...because where I was running at 600 ppm in planters was way to high for the Hydroton bed. Im now down to 470 PPM.
When I think about it...it makes sense since the roots are way more exposed to nutes.
Also some nutes can't be absorbed at 6.0---thats an organic's number.
5.8 is our number
So the strain and medium (all the things the above poster asked) are very relavent to what's happening in your garden.
My question is how are you using a 3 part series and ONLY getting 170ppm...and at what conversion . (If you aren't using RO water--that number seems impossible)
We need pics too...it may be a specific element is lacking (A lack of Phophorus is common, and some yellowing is normal).
PS: My plants are almost at the exact same stage as yours (3 weeks and 5 days in my last pics)--Check my Grow journal if you want something to compare to (just excuse my nute burn)
EDIT:--I just noticed you said 2 weeks into flowering....3 weeks in total. Does that mean you put your plants into flowering after 1 week of Veg?