I really, really suggest not worrying about levels and such. The whole point of EI is for dosing to be simple, if you want over-complication then PPS-Classic is your game, hehe. The reason behind the 50% water change is to remove leftovers without having to worry about just how much was leftover.
I, really, really suggest following this
, just dose those amounts and you'll be fine. Once you have gained the experience to really know how your aquarium is handling the fertilization program then
you can start tweaking.
That link to AQ isn't a list of recommendations, either daily, 3X weekly, etc, nor is it a suggested level to maintain things at, it's just one person asking if it is correct, without any explanation of what the numbers meant, ignore it.
If you prefer to dose using liquids, then mix up the solution per these directions
and dose as indicated.