Anyone know what these are?

[Pikachu]

They appeared like 2 weeks ago and they are mostly on the glass.

 

[Zach B]

Look very similar to flatworms from what I see

 

[tbrown]

+1 flatworms possibly acoel

 

[RocketEngineer]

Those are likely red planaria flatworms. They are a pest that can overwhelm a system. There are chemical treatments available to kill them so research those ASAP to get ahead of this pest.

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[i cant think]

They appeared like 2 weeks ago and they are mostly on the glass.

What size is the tank?
They are Red Planaria Flatties and can decimate corals quite fast (especially with a high population). I wouldn’t do chemical eradication as I personally don’t trust chemicals in a reef unless I know they don’t have ill affects.