However, instead of going himself, he sent his apprentices on the mission for a test as Jedi Knights. However, Arca discovered that there was more to the civil war on Onderon; the Dark Side was at work, so he left to join his apprentices. Once on Onderon, Arca used the Light Side of the Force to remove the Dark Side left in the city by the tomb of Freedon Nadd, Dark Lord of the Sith. However, Arca recognized the fact that Freedon Nadd still had many followers in the city, and found it necessary to recruit other Jedi to help quell the Freddon Nadd uprising.
During the reconstruction, Naddists lanuched an attack, and by employing the Dark Side of the Force, delivered a crushing blow to Master Arca. Feeling the potency of the Dark Side, Arca resolved to see the former ruler, King Ommin, who Arca learned delved heavily into the Dark Side. During his visit however, the spirit of Freedon Nadd appeared, and gave King Ommin the power to put Master Arca into a coma-like state, surrounded by Dark Side energy.
Arca was taken off by Ommin, as his Jedi apprentices were left to defend themselves. Soon, however, Arca was freed from his imprisonment by King Ommin when his Jedi and their comrades came to his rescue, killing King Ommin, and in the process, extinguishing the effects of the Dark Side. Arca remained on Onderon to continue his mission of ridding it of the evil, and sent the tomb of Freedon Nadd to the Dxun moon to be held in a highly guarded temple.
Months later, Arca learned of a group calling themselves the Krath had launched a coup for political power in the Empress Teta system, as well as waged war against the Jedi. He sent the Jedi on missions to inform the Republic, as well as confront the growing force in the Teta system. A few more months later, Arca was visited on Onderon by Jedi Knight Exar Kun, informing Arca he was investigating the Sith, and would like to retrieve the ancient Sith artifacts the Jedi discovered that had belonged to King Ommin.