I get the same thing, too. Don't know why but the only variables that I haven't tested are 1) potassium and 2) hardness. I'm guessing it's a K issue but won't know for a couple of weeks.
As I mentioned above, the specific cause of this problem is not known. There was some discussion before that it might have been a lack of zinc or another micro nutrient. Though the answer to this was not 100% figured out and the cause is still unknown.I have seen something similar to this before twice though I am not sure if it is a nutrient issue or is related to something else in the tank. There was some thought that it might have been a micro deficiency, specifically a lack of zinc. Though it might also be a toxicity of some kind.
Zapins,As I mentioned above, the specific cause of this problem is not known. There was some discussion before that it might have been a lack of zinc or another micro nutrient. Though the answer to this was not 100% figured out and the cause is still unknown.
How much of each fertilizer are you adding and how often? You mentioned "Recommended levels," but many people recommend different levels and it is hard to infer how much you are actually adding from this.
What is the water temperature?
Yes, some plants like Alternanthera look very sick! Why do you think is a micro deficiency and not something else?Looking at the pic, I suspect it's a micronutrient deficiency since there is algae growing on the leaves and it looks sickly.