EC/ppm rating

To further answer your question, sounds like you can go heavier on the nutrients for your plants that have been in flower for a good while. You could always mix up a double or triple strength batch (keeping the same percentages across your different components) then 'water down the mixture until you hit the PPM you're looking to provide for your plants. So if you're looking for something that's 500ppm or 700ppm start with a solution that's above that and water it down until you hit your target. I also use a smaller container to measure my pH and ppm, I keep my water in one-gallon water jugs and pour out a bit to test, adjust and re-test. : ) I can just stand up the tester and not have to hold it while it settles it's readings.