You can't check the ppms available to the plants by checking runoff when you "flush" your plants. Whatever number you get is meaningless.
You say you heavily amended your soil, then you added 2 different fertilizers, then you watered with teas, silica powder, etc... You also say you've been feeding them something every watering. Why would you need to add anything else? If you had a heavily amended soil like you say a top dressing of the Gaia Green is all you would have needed if even that. You should have been feeding plain water. You definitely don't need to be adding more stuff with that overpriced Elemental Roots stuff. You just said all your plants are starting to get nute burn. Now you're talking about adding more nitrogen? Why would you think feeding them more would be the right thing to do? That makes no sense.
You seem to be in the "add more" mode to fix your plants when the problem is you've already added too much.
You haven't shown a picture of the entire plant just some nasty looking leaves you cut off and many should have been left on the plant.