It's time to drop a little truth, here. It turns out that I have been completely wrong about what's been happening in my tank the last year or so. Let's start at the beginning.
When I first set up this tank, I had two 54W x2 T5HO Odyssea fixtures over the tank. At the time I was using all 4 lamps to illuminate the tank, and I quickly developed the brown fuzz.
Too much, right? Right. So, I raised them up and nearly blinded my wife and myself and we squinted to see either the tank or our nearby television in the intense glare.
So, I planned for the LED's. I designed and built my fixture to work with this tank. At the back of my mind, I always had a little doubt, nagging at my process, but never fully intruding in execution. It's not enough!
the little voice kept whispering.
I hung the fixture, proud of my accomplishment - and proceeded to watch my plants fade slowly into mush. I was so frustrated. I thought it was too much light, a CO2 issue, not enough nutrients, contaminants in my tap water, poor flow, inadequate filtration - anything but what the nagging little voice told me, because as soon as I lowered my fixture or dialed up the faders, I would get algae again!
At the peak of my trouble, I finally dismantled the (now BBA-laden) scape, and installed a low-light plant scheme that was really just an effort to make myself feel better about the failure.
It only got ugly slower.
I was breezing through the forum a few weeks ago, and came across a post by Tom Barr explaining why he didn't use LED's at the moment. I'm not sure what exactly he wrote that triggered the little whispering voice to suddenly become a shout, but that's what happened. I realized that for my LED's to be an effective method of lighting my tank, I would need to double the width of my 6" wide fixture.
As a sort of test, I removed the LED fixture, and replaced it with my old T5HO's, this time with only the 2 Geisemann lamps plugged in, and lo and behold! Almost instantly, the tank appeared twice as bright. Within minutes my Marsilea was pearling - a sight hitherto unseen since the original scaping of this tank.
Since this replacement, I have seen much improved growth and health in my aquarium. What a bonehead I have been. Denial is a powerful force, people. Instinct can often be ignored as a result. It's unfortunate that the process had to go that far, and I had to lose so many plants before realizing what I needed to do, but there you go.
The next phase (to be implemented over the course of many months, as my annual tank budget is tapped) is to expand my LED fixture to accommodate the actual requirements of my tank. This means having one emitter for every 4 square inches of footprint, and hanging it at an appropriate height as well as dimming it to the appropriate level. It will take a while to adjust, but I'm ok with that. I'm nothing if not patient.
Until then, I'll keep my Odyssea fixtures in operation, and feed my tank properly.