Best if you have osmosis water and mix the stale water for 24 hours (after 24 hours the chlorine has evaporated somewhat) to an Ec value of 0.2. Then add Cal / Mag until the Ec is 0.4. This is your source of water, so you can flush.
Look with a microscope 👌If the trichome heads are about 70% milky and 30% clear, you can start with the flush. If the trichomes are about 70% milky and 30% amber, it is a very good time to harvest 👍🙏🏻 but do not pay attention to the leaves of the trichomes on the buds 👍