What are these?

[svreef]

Just got some macro algae and within days these white things came out. Any ideas?

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[ashburn2k]

Feather duster


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[Coral reefer]

Maybe hydroids

 

[MarAquatic]

Yeah kinda looks like hydroids

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[Kensington Reefer]

hydroids
kill kill kill
they will sting everything
kill them NOW