EC even better. Tell us the EC when you mix nutes and the EC now.

If EC goes up after a day or so, Then they are drinking water.
If EC goes down then more nutes are taken up.
Nutes fallow the water line. Without water no nutes travel.

I have never seen more than a slight dif in nute uptake. The big dif is in when water levels fall and concentrate the nutes.

Plants also piss in your water or give off waste to keep the EC up. That's why no big change in nutes.