Possible Plant Deficiency? (Ludwigia sp. Red)

[Brian_Nano12g]

So I've been trying to propagate my Ludwigia sp. Red into a healthy population again since I hit the 'reset' button, so to speak, on my 6g. I've been dosing PPS-Pro w/ a little extra increase on the Micros and Phosphates... Other factors: 7hr photoperiod, Glut supplementation, and DIY co2 w/ drop checker in green/yellowish.

I was gone for a few days and I noticed that some of the Ludwigia has brown spots that appear to be spreading. Anyone know why and what the cause is?

Seems that if I let the affected leaf be, it will spread and eventually the plant deteriorates and melts. Is this a deficiency or something else?

Here's a close up on the problem:

FTS as of today (excuse the algae and BBA on the stone, will be addressed):

 

[Rivercats]

I'd say yes to a nutrient deficiency. It reminds me of nitrate or even how phosphate deficiency looks (they both look similar to me). Is the browning on just the outer edges of the leaves and spreading inward? What is your nitrate level?