Mini jellyfish?

[ISpeakForTheSeas]

Are these jellys

Either jellyfish or hydroid medusa - I'm leaning toward jellyfish in this case because the tentacles seem really short for most hydroid medusae I know, but it could be a hydroid.

Either way, unless it's photosynthetic or you have a bunch or tiny foods (like copepods, brine shrimp nauplii, coral food/small fish food, etc.) it should die off on its own soon.

 

[dodojojo]

Here's a somewhat better picture

That's an ephyra! Can't tell exactly what species it's from but def in the cnidarian family.