No you should not add nutes & here's why,when you start off with a fresh rez the NPK is balanced,the problem lie's with how plants feed,they dont use equal amounts of N P or K.
Lets say your ec of .6 breaks down to 300 ppm n,then 300 ppm p & last 300 ppm of k,this is your fresh rez starting point,after the ec drops to .4 obviously it means the plants have ate .2 ec worth of nutes,correct ?
Now what .2 ec of nutes is missing ? Is it N P or K,or how much of each nute,what happens if the plants only used all one part of strictly N so now you still have 300 ppm of both P & K,now you add nutes with the top off water & raise the ppm of P & K,it dont take long & your water can contain overload levels of several different nutes even though the ec still reads .6 which is very low,now you get burn or lock out with .6 ec.
Its much safer to just change the rez as often as possible,then you know exactly what ratios the water contains at all times.
