Ok the pictures are blue but..

[Euphrate]

The algae is green, i wonder if it's some caulerpa. I had some racemosa at the beginning but killed it (it bleached probably because of the lack of nutriments).
Could you help me to identify this one?

 

[Rtaylor]

Could be the start of caulerpa peltata or racemosa, both have the runners like that. If you had it before some likely survived and is now growing back.

 

[taricha]

i wonder if it's some caulerpa.

looks very caulerpa to me.

 

[Euphrate]

Ups, guess i'll have to get rid of her before she takes the advantage on my tank.