10-08-2009, 07:36 PM
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First thought is nutrient deficiency, probably iron but several nutrient deficiencies will cause yellow/browing of leaves so don't jump out and dose iron. Besides which, excess of iron has other problems, which I experienced many years ago and learned the hard way to use balanced ferts.
Having said that, though, with a root tab I would not expect this. If these are the original leaves from when you bought the plant, they will often die off. Frequently this occurs because they are emersed growth (nurseries raise aquarim plants emersed) although I have known submersed leaves to do the same on newly acquired plants, probably the "shock" of transplanting to differing water parameters. I can't see the base of the plant (crown) in the photo--is there any new leaf growth from the crown? If yes, I wouldn't worry.
I'm not familiar with significant leaf differentiation between submersed and emersed with this particular species; Rataj makes no mention of it, and he does for other species, nor does Baensch/Rhiel. This species is very similar to E. amazonicus, although the leaves of E. bleheri are slightly broader and sometimes less curved. But that really is of little relevance here.
Are you also using liquid fertilizer? I found this condition occurred on several of my E. bleheri when I went from twice a week to once a week wth Floruish Comprehensive; I experimented twice with the same result. I wasn't using root fertilizer then, and I still think that should be significant with Echinodorus. My advice would be to use Flourish liquid once/twice a week (once at first if you're not using it now). And provided new leaves are emerging, not a problem.