that is interesting. Tom has been helping me with some dosing information on
the APD list as I have recently upgraded from 4 x 40 Watt T12's to 6 x 32
watt T8's in a new canopy. It made an amazing difference however it has also
brought me some algae issues. I am presently batting BBA (little black or
apparently red tufts) on some of my plants and green algae on the glass. I
have started doing 50% water changes and dosing more KN03 than I was before.
I have ludwigia repens as well as Rotala in my tank. Prior to upgrading my
lights my ludwigia would basically be green like yours until it got near the
light source and then the tops would turn reddish. I have recently removed
most of it and replanted some of the red tops which have now grown almost to
the surface of my 77g tank and noticed that they remained a reddish color
almost from the substrate on up although more red near the surface. This
would seem to indicate that I do need more KN03. I have just started dosing
1/2 tsp 3 x a week so will see if this has any effect.

Your issue is two fold, you have less NO3 but your real issues is a
lack of CO2.

When you upped the lighting what else did you need to increase also?
CO2

Carbon is 40+% of the plant's biomass in dry weight, Nitrogen is 1.5%.
If you increase the light and thus the uptake(up to a point)then you
need to first deal with the CO2 before dealing with NO3.

Regards,
Tom Barr