Blue-green spot on pistol shrimp claw

[exmasonite]

Hey all. Looking for a little help with my pistol shrimp.

Quick background:

Biocube 29, started 11/12/14. Started adding fist after about 19 days of monitoring parameters. Added a fish every 6-7 days. The pistol shrimp and goby were last added around 12/18 or 19. Seemed to be fast buds and sharing the same hidey hole together.

Just noticed a weird blue-green spot on the lower/ventral part of his big left claw. Not sure if it is a wound, infection of some sort.

Have been checking parameters every 3 days... pH 8.1-8.2, Ammonia, Nitrites and Nitrates all zero consistently. Doing about 2.5 gal water changes weekly.

Have attached a pic of him during feeding. Hopefully it comes out ok.

Thanks in advance for the help.