[Algae identification] Anyone know what this is?

[yuzusama]

They seem to be pretty and harmless, I wonder if they are categorized as macro or not? How fast will they grow/reproduce and how large can they become? Thanks in advance!

 

[i cant think]

They seem to be pretty and harmless, I wonder if they are categorized as macro or not? How fast will they grow/reproduce and how large can they become? Thanks in advance!

Do you mean those neon green polyps?
If you do then they are not an algae type. They look to be colonial hydroids which can be harmful and sting nearby corals.

 

[taricha]

Agree the lowest ones grow where they would get nearly no light. not photosynthetic.