Don't know how any of my tank cleaners go with your puffer or tang, but in my 125g reef currently have
1 sea cucumber (cleans the bottom like a champ, but make sure if ya get one he isn't a tank nuker <can release toxins and kill everything in tank>)
1 Sand sifting star (seems to get along fine with my smaller hermits, but had to remove a larger hermit for chewing on the stars legs when he would surface)
100ish various small snails (mostly Nassarius). As previously stated they burrow and constantly churn up the sand.
Many people take caution and are wary introducing any crabs in to a reef, but I tend to take the "until he harms something he can stay" approach. With that in mind, smaller hermit crabs will comb all over your rock and substrate for algea and uneaten food crumbs.
Hope that helps,
Chris