The blue velvet slugs should definitely take care of those, the reason I was asking about a wrasse is because it will fare better long term. Once the slug eats all of your flatworms, it will slowly starve, and you don’t want them to die in your tank because they accumulate toxins from the flatworms. You could definitely sell it to someone else with a flatworm problem, but a wrasse (halichores or similar, not a fairy or flasher) will take care of these guys and some other pests you might have now and in the future