I noticed these guys tonight for the first time. I haven't really watched my sump at night for a couple weeks I guess. Are they good/bad? Should I get a fish to control them? I still have some room for some company in the tank.
They are not the Convolutriloba sp or the waminoa sp, which give people the most problems. So, if they are not an issue, I wouldn't intervene. I wouldn't get a fish just for that purpose. I have flatworms in my tank and they are just a part of my little ecosystem.
I have more than that. In places of calmer water they tend to really gather at the water line and just below and also right above the substrate. They bother some people to see them and they want to get rid of them. @twilliard is the one to talk to, to discuss options.