This macroalgae came in with some chaeto, what is it?

[99gtbaby]

What is it and is it something to worry about being in my sump?

 

[Adolfo]

Caulerpa Taxifolia my guess
Remove soon as possible have the same problem with other type of caulerpa

 

[99gtbaby]

I harvested some chaeto today, here’s a better look at the hitchhiking macro algae.

 

[Isopod80]

Definitely a Caulerpa sp. Some like it, most hate it and it can be very invasive. It also has a higher probability of going sexual than many other macros. It's illegal to ship to California for these reasons.

 

[WheatToast]

It's illegal to ship to California for these reasons.

Not for all species, though.
https://www.newportbeachca.gov/home/showdocument?id=1218

I posted this list of legal and (somewhat) commonly available species on a different thread:
Caulerpa prolifera
Caulerpa brachypus
Caulerpa serrulata
Caulerpa lentillifera
Caulerpa chemnitzia (was once known as Caulerpa peltata)
Caulerpa cylindracea
Caulerpa paspaloides

Caulerpa Taxifolia my guess

I agree, though Caulerpa mexicana is also a possibility (Caulerpa taxifolia has small, widely spaced "bladelets" (like those in OP's images); vice versa for Caulerpa mexicana, though the difference is quite minor).