I’ll start by saying that coco is not my strongest suit, but what I see is the plant is hungry. What you may have called toxicity could have been a lockout from accumulated salts, allowing assimilation of some nutes, but not others. Now that you’ve flushed out the salts, the plants are hungry...
Looking a lot closer, maybe a week, it's hard to tell if the buds have swollen .But it's close. Once it stops drinking water, that's a sign it's almost ready.
Just my 02 cents, but it looks like the leaves pretty much straighten out once they mature, I suspect it may have to do with nutes (too much) and/or the potassium silicate. (I've never used it). I've had seedlings do that before, and it was too many nutes too early. It didn't burn the plants...
Because of the climate (rain), it's best to grow in a greenhouse, but things grow great, because of the long photoperiod (in May it's sunny from about 4 AM to10-11PM). Southern Alaska is better, due to the warmer temps.
Oh, the dreaded flushing question. The small bit of actual research that been done on it, says that flushing removes nothing from the plant, and in blind taste tests, most people preferred unflushed weed. Why yellow the leaves and buds while you starve your plant in the home stretch? Bottom...
Kinda depends on how well your tent is sealed. If it's almost airtight, then yes, if you leave a vent open at the bottom, probably not. You'll be able to tell if the sides of the tent suck in. In my case I have two 8". exhaust fans and one 8" intake fan, but I leave a vent open at the bottom...
I just read up on Sarah’s law, it’s weak sauce and nothing like the US variant. In the UK version of the law (not really a law) you need to know the name of the person then they will tell you yeah or nay. In the US version, there’s a database you can log on and specify a distance from yourself...
If those are old calyxes that formed at the nodes, they often turn that color because they’re really old! I don’t see anything cottony or webby looking, so I’d say you’re fine.
Dont flush, it accomplishes nothing and starves the plant.
No need for three days dark, for max terpenes, harvest as soon as the lights come on in the morning.