I have kept a couple of the h. diphreutes in my reef. The first was awesome, completely reef safe for over 2 years, I lost it to an ick outbreak. What a prized fish that was! A stunning fish in the display that every one commented on.
The second is also a great fish, that is until a new fish (a blue stripped rabbit) "taught" it to eat zoas. It is still SPS safe and most LPS are safe (I have frog spawn, hammer, trumpets, even favia) but it now devoures zoas on site like an offering of candy!
Now, like with keeping dwarf angels, the constant grazing this fish does may reduce day time PE from SPS, but I have never seen my butterfly or coral beauty actually harm and SPS coral.
.... and I've been watching a long time!
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thanks, this was very helpful i think i will get one