8 weeks into the flower, I have waste in the coconut 3.5ec, can it affect the resulting smell and taste after harvesting

do you mean you are flushing "waste" the coco coir substrate "coconut" and its coming out at 3.5EC? I would continue just giving them water and nothing else till its harvest date. Its a bit high but nothing unheard of. If it was 5EC i would give it a propper flush and get around 30-50% runoff via the pots volume. The plants in the single photo you uploaded look nice. so that's a bonus and I don't see any burning or anything indacting its getting to much. But more pictures would be ideal. A good cure will bring out the flavors and accents of the herb. anything not cured and just dried will taste bad.