So I need to know what this is... is it a liverock anemone? Will it hurt my fish?
That's not good stuff. It's aiptasia
How in the world do I get rid of it and to keep it from happening?
Some species of peppermint shrimp will eat them, they come in on live rock. I've seen a girl on you tube inject them with lemon juice as well.
There's a couple of products you can get, Aiptasia-X or Joes juice that should help get rid of it. If you decide to go the shrimp route make sure you get true peppermint shrimp, some info here Peppermint Shrimp
DO NOT try to get rid of them by squashing them as this makes them multiply. I would get a peppermint shrimp as they have a huge appetite for this stuff and they're cute too. I have also heard that injecting them with boiling RO/DI water works too.
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