Ah... it is as I suspected, being a long time supersoil grower myself. You are seeing the clawing especially at the top and the little bits of burned tips, and equating this to Nitrogen Toxicity, yes?
While your leaves are definitely trying to tell you something, true toxicity looks far worse than this... the plant would look to be terribly ill. What you have are some complaining leaves.
So what are they complaining about and showing little burned tips as a result? Your roots are right now exploring that supersoil at the bottom of your container. There is a lot of very rich stuff down there cooked into that soil, and plenty left over that isn't all the way cooked yet. There are some little zones in there that have pH fluxuations that the exploring roots didn't expect... hot zones of nutrient rich and mineral rich supersoil. When a new root growth tip hits one of these, it can be pruned off and split right there to go around it, or it can adapt and move on... lots of things can be happening down there, and as it does you are going to get reactions in the leaves above that something is not exactly perfect for a young exploring plant. The leaf tips are pointing toward the roots sort of like a cat on a hot tin roof tries really really hard not to touch, or a swimmer sticking a toe into a cold pool and pulling back. If the root tip split into two, that damage will result in the little damaged leaf tips all around the plant.
Basically, this is all normal with a supersoil grow. They call it supersoil for a reason... it is really too hot for the plants to be able to handle by itself, hence the reason we put it only in the bottom third. The plants can handle this because instead of forcing the roots into a medium so rich, we are allowing them to seek the bottom and find this rich soil, and then adapt to being able to live within such strong soil. The reactions you are seeing in the leaves above are telling you that the supersoil is working... and all is well. Every supersoil grow I have ever done, and there have been many, I get burned leaf tips and this reaction to the young plants of finding the supersoil. Give them time, and they will adapt.