What's this little thing?

[reef_keeper]

Seen this a couple days ago on the glass. There are a few I can see on the glass. What are these little buggers?

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[SushiGirl]

Hydroid jellyfish.

 

[reef_keeper]

Good or bad?

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[SushiGirl]

Indifferent. They usually go away after a while in a new tank.