Brown patches in stargrass and baby tears

• pH:
• Temp:
• KH:
• GH:
• NH4:
• NO2:
• NO3:
• PO4:
• Iron:
• Dosing: 25 mL Excel, 10 mL Flourish, 7.5 ppm NO3, 0.8 ppm PO4, 5 ppm Flourish K, (3.75 ppm NO3 yesterday, approx 2.4 ppm K)
• NO3:PO4 Cumulative Dosing Ratio: 30:3.6 = 8.3

Notes:
Starting yesterday, I noticed brown patches on the stargrass and baby tear leaves. It's amazing how quickly a defiency can show up. I had dosed less N/P during the water change, but there were no brown patches on the java fern that develop with too low N, so perhaps there is a shortage of potassium. Yesterday, I added extra KNO3 (3.75 ppm NO3), and today, I added 5 ppm Flourish K (along with the usual scheduled KNO3) to see if that helps.