tds pens actually measure EC and convert to ppm -- the conversion can 1 of 3 or 4 scales, so the EC is more universal to use. From what you wrote, looks like a "500" scale which most people in the USA/Canada will also go by.. the equipment you have will dictate and that is somewhwat regional.
.48 EC (some are /1000, but same digits, this is what i'm used to) is too low for sure. at thist late stage of the game. whatever the substrate was providing before, you are likely providing now almost entirely through fertilization.
you'll find out soon.. deficiencies will creep in. Wouldn't be a bad learning experience to see where that lower threshold is so you can more easily avoid it in the future. So many variables go into how much and how frequently... inevitably it requires some trial and error on your part to get familiar with the tools you are choosing to use.
soil has a lot of unkowns and can vary more than other options batch to batch. even when comfortable, you may need to make adjustments on the fly.
vs. soilless where you control all of that and you get guaranteed analysis labels etc... the only one to blame for a problem in soilless/hydro is the person fomrulating the fertilizer. noblaming the inconsistencies of the soil products :P