ID please...

[doofus117]

Hi all,

A few months ago, these started appearing in my pico tank. They have strong roots now, turn pale green at night and back to dark green during the day when lights are on. They look like a plant but seem to have a calciferous skeleton. They look pretty cool, but not sure what they are. Any thoughts?

[noirsphynx]

Halimeda macro algae.

[hillegom]

+1
For future, here is a guide to study if you have more questions on hitchhikers.
Scroll down for the algae part

http://www.xtalworld.com/Aquarium/hitchfaq.htm