I let my tank get overrun with algae again and had to buy new emerald crabs. I always pick the good ones. Never a bad one in 10 years. Next time I'll cover the microphone with my finger so it doesn't record the audio from the shows that the gf is watching while I'm video recording.
Here an emerald crab picks off 2 med size bubble algae.
http://youtu.be/dCPHX0aVhfA
http://youtu.be/G-UeXYhiYWI