Ive used Tupur brand soil. Its available here on the West coast. They make one with zero ferts. Coco, sphagnum moss and perlite thats it. No gypsum, lime or conditioners either. Its a bitch to use if you are new or dont understand soil chemistry.
I dont know how you get N+ toxicity. Might be using a fert with too much nitrates is my best guess. Or too much coco coir. After 4 months or so the media has finally broken down enough for microbes to feed on the Carbon which leads to a nitrate dump from their waste.