Worm and flashing fish?

[KuhliCray]

So, a day ago I found this worm thing in my tank. My kuhli loaches attempted to eat it and spat it out. Keep in mind I haven’t fed worms to my tanks in 2 weeks. Also, they were dried. Anyways, I caught my smallest neon tetra flashing against a leaf and stone. They all do that occasionally actually. Any help? Nothing strange on any fish’s body, and no lethargic behavior either.
It might be hard to see, I’ll circle it if needed.

 

[Big Bubble00]

The black stringy thing?

 

[V227]

Flashing does not always indicate a parasitic problem. Often flashing can be seen after WC's due to subtle water chemistry changes. Dominate fish, especially but not limited to cichlids will flash or display to demonstrate their strength and territorial claim.

 

[KuhliCray]

I haven’t done my PWC yet, I circled it.