Captianmorgan/hyroot/natro.hydro, thanks for the replies.
First, I'm glad to hear that other folks are growing "rock hard nugs" under flouro, so whatever my issue this go-round was, it's correctable.
I'm set up in two 4x4 tents, with the lamps positioned about 16" above the canopy. I never invested in dehumidifier, but my humidity remained in the low-mid 60s throughout the run, and my temps were always in the mid-70s. My nutes were the Botanicare CNS17 line, supplemented with Botanicare Hydroplex and Liquid Karma. I ran my ppms up to about 1800 by the end of flower.
I'm also thinking either my SCROG method or my drying my have caused the super light fluffy buds. For the SCROG I never topped my plants to make multiple heads before going to SCROG. Instead, I aggressively lollipopped, pulling the top half-dozen or so branches through the grid. Then rather than allowing the branches to grow upwards I continuously wove them through the screen as they grew, so I wound up with this insanely dense canopy, with some branches like three-plus feet long.
For drying, I didn't water the plants for four days before harvest, then hung the branches from the scrog screen in the tent with the mini-fans still on to create strong circulation in the tent. Also, while manicuring the buds I worked by reaching into the tent with the 420s on for lighting. I wonder if this combination of strong air circlation and exposure to the 420 lights during the drying process dried them too quickly.
Thanks again for all your feedback!
