Something in 20-20-20 that throws off TDS???

My friend has one of those cheap TDS pens that makes a lot of sense when using Jack's Hydroponic A/B (A+B= 20-12-26 total).
But when he switched (basically a soilless growth medium) to Jack's 20-20-20, it takes at least twice if not three times as many teaspoons of 20-20-20 (as A+B combined) to arrive at what the pen says is the same TDS. I mean, starting out with water already at 200ppm or so of other stuff, 4 tsp. in 3 gal. still wasn't even quite 600ppm ?!?!
Something in the 20-20-20 not registering on the pen or fouling up the reading?

Cheaper pens need to be calibrated more often. Nab some 1000ppm solution from amazon. I saw some for like 10 bucks a week or so ago. If your still having problems after a re-calibration, it could be few things, but i'll need to know more: Your temps, dwc? dtw? ebb and flow? your lighting?

The temp is the all the same temp always that he calibrated the pen at (1000 NaCl @ 78 deg F)
Listen ebb and flow, lighting -- all that doesn't matter -- I'm saying the second he mixes up side by side (usually one or the other to pour over soilless mix but side by side just to test what's going on with ppm) and put the pen in... the one fert numbers make total sense for hydro nutes
and the 20-20-20 he's trying to move to instead of the hydro ferts since it's soilless these days not hydro setup, takes like 2.5 TIMES as much 20-20-20 Jack's regular to arrive at the same ppm the other sample takes of 20-12-26 Jack's Hydro nutes, side by side same temp, just mixed them... no other info. is relevant.
This is the second time I've asked a very straightforward question here and it's either useless irrelevant info. or you want to know my life story for no reason. Read the top again. Thanks for nothing here as usual RIU (there's probably just too many threads here but nobody answers Nutes subforum either I eventually find the answer myself)

If your using something like jacks classic in a soiless I would think your asking for micronutrient deficencies.

Hey relax. If you want to get your reading up to 1000ppms then keep adding more. Whats the question? Something not registering in 20-20-20? Impossible. Solids are solids and that's that. Get a new pen if your in doubt with that or Add till you get the ppms you want and feed your plants. Were not chemist or TDS calibration analysts. Ever think that maybe the nutrient with 20-20-20 is junk. Good Luck.