From what I read on here there are a few methods. The best one seems to do a 50/50 frag dip with h2o2( 3% hydrogen peroxide). It should bubble and kill all of the algae. You can wait for the algae to die or 30min at most. I haven't tried it with my frags (zoas) but plan on doing it soon! Good luck!
https://www.reef2reef.com/forums/showthread.php?t=52084 It will be on the first page 3rd post from the bottom. Talks about what I said. There are also numerous posts on how it didn't affect their corals at all and removed the algae take a look at it!
I have a bunch of hermits, I mean a lot (30 gal frag tank with about 60 red & blue leg). Once every 3 weeks I move frag trays to the sand bed and the hermits swarm them leaving them pristine in about 24 hrs (not that they are too bad with a cleaning every 3 weeks). I have tried the peroxide method and is does work but does not eliminate the issue and tends to upset the zoas & palys so I like the hermit method.