Snowflakes growing in my tanks.
 

Hi everyone,
I have these snowflake like things growing on my tank glass. They started shortly after introducing a couple hundred pounds of live rock. They are currently about 2-3mm across and have perfectly uniform tenticles reaching out from the center. I have a picture of it and am attaching it to this post. In the picture due to the size and the focus ability of my camera the tenticles are not visible but the bulk of the body and shape are visible.
Does anyone know what it is and if it is a good or bad thing to have in my tank? I am running mainly fish only but have also some soft coral and anemonaes.
Any help or advice would be appreciated.
thank you,
DNoakes.

Hmm
 

Are they flat on the glass? If so don't worry about them too much. I had something similar at one point and they ended up either being eaten by the fish or just disappearing. I am not sure where they went but they are gone.

yeah they are perfectly flat. I was wondering if they might be a hydroid? Not sure what hydroids are and not sure if they are good or bad. I have a shipment of starfish and urchins coming in and am worried about introducing them into that tank.

Not hydroids, but star fishes that came in with your live rock. I had them too, but disappearred after a while...eaten by fish or died. Usually pretty harmless.

Okay these things are creeping me out. They just started swimming around the tank like jelly fish. There are thousands of them.

My guess is that they are jellyfish. Jellyfish start out as polyps similar to what you saw on your glass and then release several offspring from a single polyp. If they are free swimming I woouldn't worry too much about your urchins and starfish. I'd be more concerned about your corals/fish. But since these are babies they won't really pack a huge sting, in fact, some of your fish might eat them depending on what you have. Take a picture! I wanna see, I wanna see!

+1, the life cycle of a jelly fish is really fascinating but they tend to die very easily in captivity so I would love to see some photos!

Does anyone know if there is any fish or invert that will eat Jellyfish?

I posted an attachment to my original post. It shows one pic of one of the jellyfish I will upload another pic with this message.

Here is another pic as an attachment of the Jellyfish in my tank.