Could be.

But I supose if it was a Co2 or fert. issue, I'll had some similar problems with other plants also. In Didiplis Diandra maybe. This one is allways green.

I didn't explained myself well, sorry, writting in english is a bit hard for me.

The stem in the end of the plant turned white, rot and die. Started a week ago.

Plants:
Star grass, Hemianthus Calitrichoides, Didiplis Diandra, Rotala Green, Ludwigia Arcuata, Hemianthus Micranthemoides, Anubia and Cabomba furcata.

Could it be excel toxicity? I started to have some BBA and haded some by that time, not too much, directly in some anubias and driftwood without water movement for some minutes. But this algae also indicates low Co2, I just find strange for the plant to die so quickly.