EC readings when approaching harvest.

[2ShedsJackson]

I've been checking the EC readings of my feed water and then checking the run-off EC after letting it drain out for about 1 hour. I'm following the CocoforCanabis guide by which I mean keeping the run-off EC between 0 to +300 above the input feed EC. All's been well until this week when the run-off EC has gone crazy, over +1000 sometimes +1200!!
I'm wondering whether the plants reduce their nutes requirement when they're almost due for harvest or has something else gone wrong?

[Allotrope1000]

Hi, 2Sheds.
For my greenhouse grows (50/50 coco/perlite, 7 gal fabric pots, GH Trio + CaliMagic, 6.0 pH), I never checked my EC due to swings in the local public water supply. EC is high due to hardness.
Did you check the EC of your water source before mixing nutes? That could be a possible source of your high EC readings.