Still brown patches in java fern leaves, needs Mg?

• pH: 6.8
• Temp:
• KH:
• GH:
• NH4:
• NO2:
• NO3: 10
• PO4: 0.15
• Iron:
• Dosing: 5 mL Flourish, 5 mL iron chelate (0.5 ppm), 10 mL KNO3 (2.5 ppm), 15 mL KH2PO4 (0.6 ppm), 1 tsp epsom salts (2.8 ppm)
• NO3:PO4 Cumulative Dosing Ratio: 15:1.8 = 8.33

Notes:
I'm still noticing that that the leaves of the java fern are developing brown patches, before dying off. I suppose it must be a nutrient deficiency, but I have no idea which one it could be. I'm already dosing > 30 ppm of potassium and about 14 ppm of calcium and about 4.2 ppm of magnesium. I looked back at my logs, and noticed that up to a couple weeks ago, I had been dosing some additional magnesium from magnesium sulfate (epsom salts) in addition to the Mg that comes from Equilibrium, since recommended levels of Mg are in the 5-10 ppm range. I dosed an extra 1 tsp of epsom salts (adding an additional 2.8 ppm) today to see if it has any effect on the leaves. I also chopped off the worst of the leaves.

I usually dose iron and flourish first thing in the morning, but today, I dosed them late in the day. I noticed that the green water was clearer today up to the point where I dosed the flourish/iron. Either both or one of the flourish and iron seems to encourage the green water to multiply during the day.

I also just realized today that I've been running the phosphate test incorrectly, adding too big of a water sample, which has been throwing off the results by at least 0.3-0.4 ppm higher than it's supposed to be. Oops. I should really try reading those instructions better... So, this week, the phosphate levels have been lower than I've thought.