Seems to be a bad Phosphorus deficiency mid-flower.

[Rusty Trichome]

My Northern Lights plants seem stuck on a .7 point pH drop. 7.0 in. 6.3 out. 6.8 in 6.2 out. 6.9 in 6.2 out. THis has happened three times in a row...I'm following your winter sched and getting a few ounces of runoff whether it's the 1qt water+1qt ferts or just the 2qt water. So, I measure the run-off. I am seeing the darkening older fan leaves. 'Pillowing' starts at the tips which is what I call it when the leaf surface starts to look a bit shiney and lumpy, then the margins start to turn up a bit. Travels down the fingers of the leaf Seems like the same old same old.

Might be that Fafard soil is buffered to a lower ph, needing a tad more lime to compensate. Did you ph runoff from the Fafard without the lime?
Do you let the soil dry between waterings, or are you trying to adjust ph every day?

I'm still mixing my lime into my potting soil 'dry'. I'm thinking about mixing the soil+lime in a pot with drain holes, add some water to make it more of a slurry...then stir the crap out of it before all the extra moisture runs out the drain holes leaving me with soil I can put into another pot when transplanting.

That's pretty much what I do.

Strange thing, my Laughing Buddha plants are smaller in the same size pot and show the same runoff pH as input pH. I don't know if that means anythign.

My guess is that you got the right ammount of lime in the mix on that batch of soil. (don't tell me it's the same batch, lol)