[Philosophos]

I think after a bit of pondering the issue, there's something very fundamentally wrong here. Java fern takes skill and effort to kill, or one unobserved variable VERY out of place.

A nutrient has to be very deficient or toxic here. Something very specific must be very wrong. mere CO2 issues wouldn't do it; these are tough plants. Nutrients being a little ways out of line wouldn't do it either, these plants live in tap with inert substrate, fish food, and general neglect. I can't see it being broad, combined toxicity; there are other plants in this tank alive and well. If it's something quirky and specific, removing variables and simplifying the system will help.

Iron toxicity from fertilizing more than every six months? How was it Hoagland kept his plants alive with .5ppm Fe then? The symptoms certainly don't show toxicity or deficiency. This plant won't die at twice that rate.

Not enough or too little light? I've seen java fern hold up between .75wpg and 4.0wpg+ under many kinds of light, with synth periods between 12 and 6 hours with or without synth breaks. I'm sure many others can attest to this. Award winning tanks are grown anywhere between 8 and 12 hour photo periods with and without synth breaks all the time.

What we've got here is a variable stew (yes variable, not veritable). How about trying to remove as many unnecessary variables as possible? Those root tabs can go. Java fern can grow strapped to the side of a log, and you've got aquasoil in there now. There's a pile of fert brands running around, perhaps try consolidating and refining the method; the toxicity may lay there.

You could also try calculating the ppm's for everything you're dosing, and measure the degradation rate of the root tabs. You may be able to rationally figure out where the most likely problem is, if that's the sort of approach you like.

How frequent are your water changes? May I suggest trying a mass water change as a re-set to what ever toxic may be floating around?

Check your fish food. Compare it to high end brands. Anything seem out of place?

I think a stable, tested method to start from will help here. After you've got it established, then try playing with everything else. It's much easier to start stable than to chase variables around.

Pictures would also be nice. What you tell us you see might not be the same as what we observe of your tank through a few photos.

-Philosophos