ID Please

[PortSideReef]

I was changing the water in a 10gal tank used for emergancys/fish purgatory/quarantine as needed and notice these. I have no idea where to start asking Google what they are. Anyone able to ID please?

 

[Sasha T]

Bit of a guess as I've never seen them myself, but they look like jellyfish, or more specifically the mobile growth stage of hydroids (so "hydroid jellyfish")

 

[PortSideReef]

Bit of a guess as I've never seen them myself, but they look like jellyfish, or more specifically the mobile growth stage of hydroids (so "hydroid jellyfish")

Searching hydroids and I think you're right. They appear harmless. I don't see any in my main tank so will let them be in the 10 gal for now and see what happens. Thank you.

 

[scubasteve]

I can't tell on my phone but if the look like little badminton birdies they will agitate fish and coral. Hydroids can hit plague proportions fast at times and they do pack a pretty strong sting.