Pest or beneficial?

[FDdragon]

Hello everyone! It's been a while but I finally received my house items and got a small tank setup foe my office.
I bought some live rock yesterday (expensive as hell!....$20 for a kilogram) but not a lot of options yet so I paid for it. Ha ha

Anyway, so day two with the rock and it looks like I have a lot of tiny jellyfish (maybe ctenophores?)....probably around 20-30 of them floating around.

I've never had these before and couldn't find much online about them in reef tanks. So wanted to see if anyone has ever dealt with them and are they good or bad to have in the tank?

Some species are predators so worried about keeping them. But if they are not a worry, it would be cool to have these guys floating around.

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[Kris]

Did you use NSW to fill the tank? I wouldn't expect these to hitch hike on the rock as much as the water.

[FDdragon]

Nah, I mixed. I did have a little extra water that the rocks came with. They wrapped the rocks with wet newspaper and then threw a little water in the bag for transport but it wasn't much.

I didn't add the water though so must be been with the rocks since my tank was empty prior to the rock.

[Livinlocal]

They look to by a type of hydroid. I forgot the specific name but these are common in new tanks and will deminish with time.