I don't know if this helps, but this type of stagnation happened to me once. My tank was absolutely jampacked with plants, and the circulation was almost nil. I had also made an auto-doser for my ferts a few weeks earlier. I tossed the auto-doser, switched to Seachem ferts (and followed their instructions) and Seachem Excel (and overdosed it for a while) and really whacked back all my plants. With a few waterchanges and a few days things were back to normal. I still do my own ferts, but I keep some Seachem stuff around for when I decide to change things up a bit and end up screwing things up.
I knew that something I had been doing had resulted in a long term failure. So I just rebooted my aquarium, basically. Whatever I had done wrong was undone by redoing all my tinkering.