I use ppm more for a reference, not as a determination of where my TDS should be at a certain week. I watch my plants more than my meter. As far as transitioning to flower, that's no big deal. My TDS going into flower was about 550ppm, even though the chart says I should be around the 900ppm range. That was from veg nutes. When I flipped, I just started feeding flower nutes. There should be a transition between the nutes when flipping. I lose 2 1/2 gallons a day. Every two days I add 5-gallons water, a teaspoon or tablespoon (depending on where the grow is at), and 5mil pH up. Over time, the veg nutes will fade out while I'm adding flower nutes.