what kinda macroalgae is it ? beneficial ?

[angmoh]

thanks

 

[Fluff]

Some type of Caulerpa sp. perhaps. Check here. There are several different species.

http://www.botany.hawaii.edu/GradStud/smith/QUEST/limu-studyguide.htm

I believe most macros are beneficial but some tend to grow so rapidly and take over the tank. Manual removal is your best defence.