Triggers in the Genus Xanthichthys are generally reef safe - with caution (always a disclaimer lol). The genus includes: Blue Throat, Sargassum and Crosshatch that we generally see at LFS. You will always hear success and horror stories. It really depends on the temperament of that specific fish. Just like some have had success with specific Angelfish in reefs.
From my experience; I've never had an issue with the Blue Throats or Sargassums that I've kept. Singularly or together. As for pairs - I've had both in my time. At least what I thought were a pair of Sargassums (one was brighter and one not so much). Blue Throats are easier to distinguish between male and female. My friends have kept Crosshatch, Pink Tails, and Nigers without issue (except for one case where the Niger got a taste of cleaner shrimp....and never looked back).
Currently; I have a Sargassum and Blue Throat together with what I consider success. The Blue Throat was introduced first and then the Sargassum a few months later. It's been several months and there hasn't been any aggression towards one another or other tank mates - including LPS, SPS, Anemones, Cleaner Shrimp, Porcelain Crab, Pistol Shrimp, clams, smaller fish such as Hasha Goby and Rainford Goby. That being said...there is the occasional empty snail shell that appears in my display. But for me...that's a natural and relatively cheap meal. It could easily be the pistol shrimp or six-line wrasse that's gotten the snail hunger.
Both of mine swim out and aren't generally shy. But I also agree with previous posts that the Blue Throat is generally a little more shy and 'chicken' (it hides a little more) and that the Sargassum is generally a little more skittish (it's startled and darts around more).
This may not have helped much since there's a lot of generalities; but if you really like triggers as I do - be patient and try it out. They have a lot of personality. If you do decide to mix things up; I think you may have a little more chance of success if you introduce the Blue Throat first and then the Sargassum. My Sargassum is a little bolder than my Blue Throat - always has been. If possible; perhaps introduce your clams in to the display first as well?
Also; as a side note - if given the choice between a Hawaiian or Indo (or other geographical location) Blue Throat; I'd choose the Hawaiian if all other factors were equal (like health and they were both eating). Hawaiian Blue Throats seem to be richer in colouration in my opinion. Cheers.
I've stated it before in other posts....pictures were taken with a camera phone and the quality isn't that great.
