Problem with Amazon Swords - news leaves are clear & rotting

I've got three Amazon Swords in a planted discus tank and the new leaves 
are clear and rotting.  I assume I'm deficient in some element/mineral, 
but I'm not sure which? My other plants (vallisneria, cryptocorynes, 
ceratopteris, anubias, and microsorum) are all fine.  Unfortunately, I 
don't know how much K and N is in the tank.  Is this sign that I need to 
add more Fe?  The water parameters are: ph 6.6, kH is 3, GH is 60ppm, 
Nitrates are about 12.5 mg/l, temp is 85 degrees F.  I have 120 watts of 
lighting over this 50 gallon tank and I am using a DIY CO2 reactor. I do 
add Flourish liquid fertilizer every other week and I am using Kent's RO 
Right (water from the tap is soft).

Thanks for any comments and you can email me back directly,
Walter P. Wu
Vanstar Contractor
Office:	wu000016 at mc_duke.edu
Office:	wwu at CL0256_MHS.CompuServe.com
Home:		Chunker at worldnet_att.net

"I hold the paper up to the computer screen, 
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