Any idea?

[John D'Amico]

What kind of algae is this? Best critter to take care of it?

 

[Fish Styx]

What kind of algae is this? Best critter to take care of it?

Looks like Ulva. Here's a good thread to peruse:

Thread 'Ulva infestation options?' https://www.reef2reef.com/threads/ulva-infestation-options.642974/

 

[BristleWormHater]

Looks like Ulva. Here's a good thread to peruse:

Thread 'Ulva infestation options?' https://www.reef2reef.com/threads/ulva-infestation-options.642974/

+1 for ulva