Melting A. reineckii leaves

• pH:
• Temp:
• KH: 5
• GH: 9 before dose
• NH4:
• NO2:
• NO3:
• PO4:
• Iron:
• Dosing: 5 mL Flourish, 0.5 ppm iron chelate, 2 tsp CaCl2 (+ 5 mL Flourish/0.5 ppm iron chelate at night)
• NO3:PO4 Cumulative Dosing Ratio:

Notes:
I just noticed that a lot of the Alternathera reineckii leaves are suddenly turning transparent and melting away. This must have happened over the past couple days. What's going on?? Was it because of the UVS causing some mineral deficiency? Or could it be because there's not enough magnesium?

The leaves pretty much turn transparent (but still red) and then melt away. It looks like what I would expect from a nitrogen deficiency, but I've been dosing a lot of nitrates for the past several weeks, and it's never melted like this before. The melting leaves seemed to be scattered through the plant, it's not obviously on the lower half of the plant, though I don't see any new leaves with this problem, so perhaps it is affecting the older leaves. That would perhaps indicate a deficiency in nitrogen, magnesium, or perhaps potassium.

I plucked off all the melting leaves off, to see if any more leaves start melting. If so, then it's probably not due to the UVS, since I turned it off yesterday. If the melting continues, I will dose some more magnesium.