Dark Spots/dying leafs.

This does not appear to be nitrogen issue but a general over nutrient issue. A lot of mistakes people make with soil is they will add enough water and nutrient mix to saturate most of the soil when best practice is to give it enough that it washes out any excess salt build up in the soil left over. By salt I mean nutrients because most of these nutrients we use are salt based. So my guess is you have been slowly stacking more and more salts (nutrients) in the soil without washing them away. I suggest you mix up a few gallons of pH balanced water and give her a good flush. This will remove any excess salts (nutrients) out of your soil. Then start doing the overwater feedings to where 10-20% comes out the bottom every watering. I hope this helps.

Nitrogen does not effect tips like this on top first. This looks like nutrition burn. My question is are you getting adequate run off when you feed to rinse out old nutrition? It looks more like nute burn starting by the curling up, and in of tips.