What type of flatworm am I dealing with?

[Rick's Reefing Adventures]

Hey!
Due to a recent move and some health issues, I haven’t been able to give the tank the attention it normally gets. During that time, I had a frag delivered and—yeah, I skipped the dip. Fast forward to today: I noticed the tank was getting way too dirty, so I started a deep clean… and found flatworms everywhere. I’m not sure which type they are—they’ve got the shape of ghost flatworms but the reddish-brown color of the nastier kind. If it’s the ghost variety, I’ll leave them alone, but if not… looks like I’ve got a fun challenge ahead.

This is without a orange filter with blues.

 

[Fish Styx]

White lights would help, but I'm fairly certain that is an Acoel.

 

[Crabs McJones]

Acoel

 

[Rick's Reefing Adventures]

White lights would help, but I'm fairly certain that is an Acoel.

Are they harmfull? How do I get rid of them? Sadly can’t fit another fish in this tank, and chemicals aren’t my first choice of action.

Acoel

^

 

[Fish Styx]

Are they harmfull? How do I get rid of them? Sadly can’t fit another fish in this tank, and chemicals aren’t my first choice of action.

^

Not particularly, no. If you aren't dealing with numbers in plague proportions, I would recommend maintaining good water quality and their population should self limit. Siphon the ones you see out when doing your regular water changes and monitor.