Seattle released Atkins, a 2007 fourth-round pick, to meet the mandatory reduction to 53 players.
Atkins has been out of the league since then, a bit of a surprise. Atkins is 6-foot-4 and about 270 pounds. He played defensive end for Seattle and had 2.0 sacks in 2008. He will presumably provide depth and insurance for the 49ers.
Balmer underwent shoulder surgery Wednesday morning, the 49ers announced.