I've got a Rose Sword (Echinodorus 'Rosé') with a few minor issues. It's got
a one leaf that is going brown around the outside edges, a few other leaves
with brown spots and one large leaf that looks like a screen door. The
screen door leaf is the one where the loach and Otos hang out, so this might
be plain old nibbling. I've read that these plants develop brown spots on
the leaves before changing colour, but the brown spots appear more like dead
spots (holes) than colour changes. I suppose these could be nibbling too,
but I don't know why one leaf has gone completely brown around the outside
edge.

Does this sound like a nutrient deficiency or nibbling?

I also clipped off one leaf that appeared to have gone pale brown, but when
I got it out in the daylight it was actually a beautiful pale pink. DOH! I'm
mildly red/brown colour blind.