Members of the family: Haliotidae (Abalones) are perfectly reef safe animals.
They unfortunately are nocturnal and feed on microscopic and filamentous algae. You can substitute with a product such as DT's or very fine pieces of macroalgae. They should be kept in an area of your tank with excellent circulation.
David,
Recommending phytoplankton for an abalone???? :? They're not a suspension feeder are they?
I think a well established tank should have enough microalgae to keep a juvenile fed for a while, but you should find out what species you have and how large it gets. At adult size it would need to be fed large pieces of macroalgae and would be pretty much useless as a microalgae grazer.
Depends on where you got them, some are temperate species, and won't last long in tropical reef. Examples are those abalone harvest near the California shore.
I have 2 about a year now. One I can see every day the other comes out at late night. sometimes I buy a rock with some seeweed on it and they clean it up. Its amazing how they return to their same perching spot every day. They are like turbo snails though, They move things around for you.