Koch was optioned to Triple-A Reno following Tuesday's start.
Koch will return to the minors after spending the past two months in the Diamondbacks' rotation. Over that span, he logged a 4.40 ERA and 1.20 WHIP with a 38:17 K:BB across 71.2 innings. Though his raw numbers were solid at the onset of his promotion, the right-hander has been been streaky throughout his time with Arizona, including an outing against the Angles on Tuesday during which he allowed five earned runs off seven hits, two walks and two hit batsman in 5.2 innings. Koch will receive regular starts in Reno moving forward. In a corresponding move, Jake Barrett was recalled.