When it comes to maintaining a healthy reef tank, many aquarists will agree to it that there are many intruders that are a threat. Some are disastrous in the long run while some cause instant debacle. Not all intruders are crooks and neither is every one of them friendly. While some worms are an absolute pro to reef growth and keeping the tank algae free, there are some, that have adverse effect and you better kick them out before they start bothering your marine creatures. One such intruder is the Flatworms. While some species are actually beneficial to reef tank there are two major species that bring in threat with them – brown rust flatworms and Acropora eating flatworms.