the ec changes cionstantly depending on the stage of the plant and the species grown
here is a simple guide that we all use followed by a way of maximising the feed,
clones 0.45 to 0.95
veg
0.95 to 01.20
flowering from 1.40 to 2.00
the amount of soluttions needed to achieve these levels depends entirely on the quality of water you use!
to maximise in the growth [veg] and flowering stages only, daily increase the EC value by say 0,25. keeping a good eye on the plants, at the very first sign of nute burn,at the tips, back of by 0,25 and your at max the plant can get!
always change the tank once every week! fortnightly will impeed on the water quality unless you have a very large water resevior and very small system, and during flowering the streangth will be increasing with the use of boosters like npk 13 14 or similar!
good luck

welcome to the world of endless possibilities,,,,,hydroponics!