hydro requires ntrients in the solution at all times. you my want a lower concentration the first week or so, but the best concentrations for soilless/hydro are not high concentrations to start. They are generally safe levels even for younger plants when done right. So, if you are restricting nutrients, that is at least 1 cause of the slow growth observed.
you shouldn't 'try a bit of nitrogenn' ... in soilless/hydro you provide 100% of the nutrition at all times. You may need a slightly different formula at various points, but day-to-day mad scientis is not required.
whatever source you're using for information is suspect. You need a better foundation of knowledge