When are they most common?

• They are most visual in a new aquarium or with the introduction of new coral.

• They are only really a problem if the coral is already stressed. Are flatworms really much of a problem?

• There are non-parasitic and parasitic forms (some parasitic species are identifiable by a line that runs down their back) of flatworms but either should not pose much of a problem to a

healthy coral in a healthy tank.

• Some parasitic types seem to make more impact than others do, so keep a stern eye on their progression.

• The main worry is if they are able to reproduce to the point where they smother corals.

• Non-parasitic forms pose very little threat if the water conditions are favorable.

• Some non-parasitic forms feed on damaged corals.

How do you limit their introduction to the aquarium?

• Inspect any coral that you wish to buy and avoid it if you see any sign of flatworms. The piece is to be avoided not so much because of the flatworms but more because the coral is possibly

not healthy in the first place to have been able to contract them.

• Quarantine tanks are helpful to enable you to observe the new piece before it is added to the display.


How do you rid a coral of flatworms?

• Increasing pH (8.4) and salinity (1.024) can reduce flatworm numbers.

• If the coral is totally infested you can give it a freshwater dip for about 10 seconds. While it is in the fresh water shake vigorously.

• You can try to wipe them off with a toothbrush.

• You can also try turning off all the lights for a while and place a piece of mirror into the tank with a string light aimed at the mirror. You may find that some species are attracted to the

light and will gather on the mirror, in which case you may remove the mirror with the flatworms on it, clean the mirror and try it again.

• Some individual Wrasses, Gobies (mandarines), Blennies, snails and starfish will eat flatworms.


Can you use chemicals to rid flatworm?

Yes some chemicals will kill flatworms but I don’t recommend using them because dead flatworms can release toxins.


What are the advantages of having flatworms?

They can be good scavengers. What are the disadvantages of having flatworms? They can reproduce extremely quickly and can smother corals.


By Paul Talbot