Not sure What to say about that, as I still see a bunch of new growth. Is it happening with the New growth as well? I'm No expert but it seems to be some type of defiencency. I'll wait for some of the others to chime in, as I am accustomed to browning but not this.
Well, I guess we are kind of on our own with this one so I did a little fishing around And it appears that there is some type of iron defiecency. Here is a link where someone else recieved the same diagnosis
http://www.barrreport.com/showthread.php/10365-My-Swords!-Deficiency-burns-or-snail-snack As a remedy I do know that flourish sells various forms of iron, And on some of the Planted tank forums that I occasionaly lurk on I've read of people putting a nail in their tank to rust. Happens a lot in Aquaponics also. But most of us are fish over plants so do Your research before attempting it.