No you want to time the magnesium levels perfect, you want the plant to have used up all magnesium 2 days before harvest. I feed molasses to my plants, and my last feeding is usually 3 weeks before, then maybe, just maybe, do half the amount I normally do with 2 weeks left. Magnesium is what makes your smoke harsh. As far as the ppm goes I couldn't tell you, soil and stuff. but yeah, usually want all metals flushed 2 weeks before. If your leaves are yellowing with 2 weeks left, you stopped feeding too soon. If they start to yellow with 7-10 days left just keep giving it water to flush that shit. Idk, that's what I know about soil at least. I'm sue the magnesium levels should be the same towards the end

WOW!!! thanks a lot...there is some slight yellowing on some of the lower leaves..Okay.. I will cut the cal mag entirely and feed one more but with nutes at half strength...I hate and literally despise bad burning black ash weed.. YUCK!!!

agreed!! with experience you can usually tell by the smell of the bud, but that's only after it's dried and cured.

If you have 2 weeks left I'd give them Half a feeding, just make sure to flush. You can flush at any point after the hairs start to get a little bit of color, I mean, you can when they're getting long and already white hairs and are just starting to turn, but if the hair has color Start flushing definately. If it's starting to turn colors then you asked at the perfect time.

Thinking of making the switch to coco/perlite here myself...so I'm listening aswell :)
In peat/perlite, I usually give water/molasses, no nutes, with no runoff, in the 3rd week to go...so not a flush, but it starts diluting the container contents...2wks to go, hard flush down to under 200ppm(tap is 80ppm here)...one half dose of molasses...10days, flush to 100-120(which is about as low as it will go)...water only till chop. This has provided my cleanest smoke to date.
Does coco flush quicker than a peat/perlite mix do you guys know? Should I change that routine ya think?

Thx and Cheers

If you experience any harshness in your smoke I'd cut back the molasses a few days each time until it's very clean. Magnesium ia what gives bud the harshness, and that's what molasses is for... So if it's ever harsh just expirement with how your molasses. Sounds pretty solid though.

But as far your medium question I cant answer that, check the buoyancy, or not that but how well it absorbs water. osmosis or somethin.