Need Help identifying: forams? hydroids?

[Triggerfish88]

I am a first time reefer after many years of freshwater. I am in week 5 after nitrogen cycling a new 125 gallon tank. I woke up yesterday to an explosion of these white things on the glass. I was at first excited thinking they were copepods, but they are not moving. Claude (AI) suggests they can be hydroids or forams. LFS says they are "normal" and a scooter blend or mandarin will eat them.

What are they? Where did they come from? How do I get rid of them?

Dry rock
Carib Sea live sand
20 lbs Tampa Bay live sand
2 jars Algae Barn copepods

All fish/invertebrates have been quarantined except for the snails from algae barn:
4 clownfish
1 royal gramma basslet
1 cleaner shrimp
2 peppermint shrimp
1 pistol shrimp
1 yellow watchman goby

a few dozen snails (Algae Barn)

All water chemistry in balance per Serious Reef recommendations.
Salinity 35 ppt
pH 8.1
Alk 7-9 (still figuring out how to dose baking soda evenly)
Ca 445
Mg 1330
Nitrate 10.6
Phosphate 0.13
I use RO/DI water, 0 TDS

Filtration:
roller filter
Protein skimmer
Refugium (red ogo, chaeto)
UV (set for fish parasites)

Thanks,
Derek

 

[tbrown]

Zooming in a little on the picture they do appear to be a Medusa stage of a hydroid. They'll likely explode in numbers at first and then, as the tank settles, they'll start disappearing.