Yes you do need them. In Hydroponic more so then dirt farming you need to watch the Ph closely. You only really set the TDS when you change or mix nutrients and that should be every 7-10 day's. The Ph needs to be adjusted every day or sometimes twice a day to keep it in balance. Ph problems are some of the first to show up in Hydro.

Do you clean and wash your reservoir in-between water changes? You should you know.

Hey it's only a plant so have fun with it growing it and then smoking it.