I was doing some maintenance on my aquarium. I have a 40 gallon all in one. I took some macro algae out of my refugium and put it in a bowl of salt water and when I did, I noticed that I have red flat worms living in my refugee. I’ve never seen them in the display ever. How much of an issue is this?

They use Photosynthesis and can multiply fast but - IMO - no problems because there is fish that eat them.