Castro asked arbitrators Matt Goldberg, Gary Kendellen and James Oldham for a raise from $4 million to $5.25 million during Monday's hearing, and the Astros argued for $5 million. A decision is expected Tuesday.
The 28-year-old was an All-Star in 2013. He hit .211 the past season, his lowest average since his rookie season in 2010, and had 11 homers and 31 RBIs. He made 102 starts at catcher and threw out 36 percent (24-of-66) of runners who attempted to steal.
Castro started all six of Houston's postseason games and hit .063 (1-for-16).
Nine players remain scheduled for hearings through Feb. 19.