barclaya holes

[<envisible at earthlink_net>]

hi all - i was hoping someone could help me with my barclaya longifolia (red)
problem.  I have a nice big specimen that i've grown quite well from a little
bulb. it's still putting out nice new leaves slowly but a lot of the older
leaves have begun to get holes which gradually widen and destroy the leaf. i
generally don't mind if an older leaf dies here or there on a plant but in
this case it's getting so that many of the leaves are disintegrating. the
plant does have a couple of flower stalks which i've left on in hopes of
propagation - i know this takes a lot of energy and can slow the growth of
leaves, but as i mentioned it is still putting out new leaves. i have read
somewhere that this effect in barclaya is attributed to excess co2, but i'm
not really inclined to believe that (i do use canned co2 but the amount is
quite moderate). tank parameters as follows:

pH 7.2
KH 7
GH unmeasured but probably low to medium hard
PO4 kept around .5 - 1 ppm
NO3 5-10 ppm
traces dosed with flourish or kent freshwater plant by measuring for iron to
.1-.5ppm
lighting is about 2.5 w/g nofl

i don't dose K2SO4 and i wonder if this is it

any thoughts?

elie