Ludwigia repens?

I have a plant , I think it's Ludwigia repens,but I'm not sure. Pics at the end of the message.

The leaves are reddish underneath. It looks like they are growing nicely, But I see that they make roots at the node just above the ground, and the stem below that node gets brown and dies, and then rots, then the plants floats.
What could the problem be? I don't have a pic of the rotten stem. I just broke it off underneath the new roots and planted it again. I have 3 small cuttings of it in the QT which also has roots, planted in a pot in a mixture of aquarium gravel and sand, with the hope that it can get big.

I have been dosing Seachem Flourish Excel but I stopped with it because I think it's causing some plants to "melt"

----------------------------------------------

 

nope - no need to blame Excell dude.... you just experiencing a common phenomena among recently transplanted new plants - also as it adapts from emersed,hydroponic culture to submerged cultivation.... dont worry - it should take and go "bos" pretty soon.

 

Haha "go bos". Cool thank you.

 

Does this plant also need heavy ferts in the substrate like Amazon Sword and Crypts?

Here's the rotten stem again. I saw that the plants does not really make nice new roots at the bottom as apposed to my H. difformis making heavy new roots.

I guess I'll have to get some good ferts and root tabs/clay balls as this plant also becomes more red with iron.