I use Dyna-Gro Orchid Pro (liquid) at 1:1500 in RO water; this gives a TDS reading of 200 ppm. I am also now adding Dyna-Gro ProteKt also at 1:1500.
These provide the trace elements that I need when using RO water. I have been watering once a week with this but will increase the frequency soon for Spring/Summer.
Later, when I find the time, I will use individual chemicals to prepare my own liquid fertilizer with trace elements.