Tank Mates for a checkered puffer

[BICvolunteer]

Hey all! Completely new to here so forgive me if this is the wrong place to ask. Where I volunteer we have a 150 gallon tank whose current 2 residents are a checkered puffer and a sea cucumber.
We’d like to get more in there but I can’t find information about what would be good to house in there without it being eaten. We already lost a crab or two and don’t want to lose anyone else so help would be appreciated!