Geltz pitched well for the Rays in 2015, going 2-6 with a 3.74 ERA in 70 appearances, but he's struggled this season.
Sunday afternoon, he allowed his seventh home run of the season when Victor Martinez hit a two-run homer to left. He's given up runs in six of his last nine appearances.
"He's in a tough stretch," Rays manager Kevin Cash said. "Figured get him down to Triple-A, let him have some success, feel good about himself again. We know he's a pitcher who can help us out simply because of what he did last year. The type of attitude that he has, he'll get back to being in a good spot."
Geltz is 0-2 with a 6.06 ERA in 17 games this season.
"I'm not going to lose any faith," Geltz said. "It's a demotion, but it's for a cause. There's a reason for it. It's just performance. ... Can't expect to stay up here with that."
Bill Chastain has covered the Rays for MLB.com since 2005. This story was not subject to the approval of Major League Baseball or its clubs.