Red Planaria, also known as flatworms, are a common reef tank pest that most reefers will have to deal with at some point. Red Planaria are small creatures, generally about 1/8th of an inch in length, that are rust brown in color. In small numbers they generally do not pose a threat to healthy reef tanks, but if they begin to reproduce in large numbers problems can arise. Not only can they irritate corals but they also consume detritus that is then not available for more beneficial micro fauna such as copepods. There are also species of flatworms that prey on specific coral types, such as euphyllia or acropora eating flatworms.
In addition to the fact that the presence of large numbers of flatworms can irritate corals and be a visual distraction, they also release toxins when they die that can cause significant damage in a reef tank if a mass die off occurs. For this reason, it is generally recommended that manual removal and natural predation be used to control an outbreak in an aquarium before using chemicals. Fortunately, due to their abundance in the natural environment there are many predators that have evolved to consume flatworms. Common options include reef safe wrasses, such as the Six Line Wrasse, and the Blue Velvet Nudibranch. After removing as many flatworms as possible, dosing a product such as Salifert’s Flatworm Exit will kill all the remaining flatworms in the tank. To avoid harm to corals, or even a tank crash, from the toxins that will be released it is important to remove as many flatworms as possible before using chemicals and to perform a water change about 30 minutes after dosing, as well as running activated carbon for a few days afterwards.
Sixline wrasses love to eat flatworms !
Dipping corals in a high quality coral dip before adding them to the display tank and choosing dry rock over live rock will both help to reduce the likelihood of introducing flatworms into the display tank. Fortunately for reefers experiencing a flatworm outbreak, there are a number of effective chemical and natural methods to eliminate them.