With every transplant, it's always useful to water the roots with Great White. I give 0.5 - 1g once a week until a week before the harvest. Every time the soil gets too dry, the population decreases a bit, which I compensate for with weekly additions. Drybacks are useful but can harm the population. If you're working with Blumat or Autopot and the soil is consistently moist, you don't need to add Great White every week, although it won't hurt either. In summary, add it once a week, and if the soil dries out more, just refresh the medium with microbes again.