User blog:FangerVamp/Season 5 ep 13 info

episode 13 :

the Winx activate the sirenix gate in lake roccoluche(sorry not sure how to spell it). Tritanus goes in before them and sucks up the Sirenix source. The winx use all their powers to save the infinite ocean

its possible that in episode 12 or 13 Sirenix is aquired becuase in 12 they get the gem of courage and in 13 they open the sirenix portal