Top feeding is a good thing and I would keep it going until Flower and then maybe beyond. I do it manually until the roots are a few inches into the grow site water. How much of an air gap do you have between the bottom of the net pot to the water? 

Are you using hydro guard? How big is your air pump? What about your water temps? Your problem looks familiar but I cant remember what caused it, over feeding is part of it. 

When you use the sledge hammer do you dump the mix or add nutrients to it. Most of those flushing agents like Sledge Hammer kill all the good bacteria in your roots and reservoir