What is bubble guppies season 6 episode 21?

As an AI language model, I do not have real-time information about episodes of TV shows. However, I can provide you with some general information about the animated series "Bubble Guppies." It is an American-Canadian preschool children's television series produced for Nickelodeon. Bubble Guppies is highly popular among children and focuses on the underwater adventures of a group of mermaid-like creatures called "guppies." Each episode typically introduces a new concept in science, mathematics, or social studies, and has catchy songs, dances, and CGI animations to enhance children's learning experiences. Please note that any specific information about an episode of the television show must be obtained from official sources or by watching the episode.