I'm hydro not soil but I can tell you , you need to learn way more about watering. My soil buddy says waterings should be twice the amount of the container so as to completely saturate the soil and help wash out contaminates.
By only wateing a 1/2 gallon you may think it's wet and it is on top but very dry deep down where the roots need it most it's not. fertilizing maybe the same only localized on top and not deep down.

just a thought.