This is good to use as a foliar spray, apply to the underside of the leaves.
This allows the co2 to be breathed in through the stomata.
I have used seltzer water up to the day of harvest, it will darken the hairs sooner than normal, and I try to focus primarily on the leaf while spraying.but don't let the color of the hairs influence your decision of harvest. Look for gland color and plump calyxes for that. but I have stopped since I have a Co2 burner now, and don't require the extra Co2 at 1800 ppm already.