Volstad, the team's first-round draft pick in 2005, was optioned to
Class AAA New Orleans on Saturday, a day after laboring through another loss. In 20 starts, he's 5-8 with a 5.58 ERA, which was the third-highest mark among big-league starters.
Volstad, who has yet to pitch an entire season in the majors without getting optioned, will work on staying consistent with his arm slot.
Last year, he was demoted to New Orleans for three weeks then came back and went 8-1 over his final 13 starts.
"Randy [St. Claire, Florida's pitching coach] said he had a similar situation last year where he went down and corrected it and came back and was lights out," manager Jack McKeon said before the Marlins' 5-4 win over the Mets on Sunday.
"Maybe that'll help him. But he has been in-and-out inconsistent. Whether the arm slot problem is causing it, I don't know."
The Marlins will need a starter to plug Volstad's rotation spot, which comes up Thursday in Washington. In the interim, they called up right-handed reliever Jose Ceda from New Orleans, where he was 2-1 with a 1.26 ERA and 23 saves.