Look, I'm no plant expert by any means, but I had a similar problem with a similar plant and the problem persisted until I started putting c02 in the tank and had proper lighting and fertilization.
I don't know anything about the brand of fertilizer your using, but assuming it's good, I would say the only thing missing from this puzzle is Co2.
If your running as much light as you are, your plant is going to want to grow fast, and it's going to need c02 to do that, without it.. it's basically suffocating.
When I started adding co2 in.. I clipped all of the brown/holey/bad looking leaves and what happened was the nice healthy baby leaves sprouted up very quickly in their place and they have stayed healthy and green ever since.
Until you can get your reactor properly set up (assuming you have everything BUT a reactor) why not just attach your air line to an air stone in the mean time? I mean.. in my mind something is better than nothing.. right?