Help with rotala

Does anyone have any ideas about my R. macrandra's problem of some leaves turning white and partly melting. It is only a small problem on most stems, but one stem is particuarily badly affected. Its new growth has turned all white and is melting away.

For nutrients: I dose KCl, K2SO4, KNO3, phosphates from enema, Seachem Trace. I dont think its the lighting since it seems to be happening on areas with good light exposure. I did uproot and replant that really bad stem, so that may be a factor. I have co2 going at 1 bubble a second and about 20-25 ppm according to the chart.

Seachem Flourish Trace on the side says various small ammounts of Zn, Mn, Cu, B, Mo, Co, Rb, Sn, and V. I also add epsom salts for magnesium. The green plant is star grass or Heteranthera zosterifolia.

KCl is Potassium chloride (K=Potassium). I have potassium going into the tank in the forms of potassium chloride, potassium sulfate, and potassium nitrate. I dont dose any Fe, but i am using flourite substrate.